Large Hadron Collider

Large Hadron ColliderExperiments, Technology, Theory and Future Contents 1 Overview 1 1.1 CERN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1.1.1 History . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1.1.2 Particle accelerators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 1.1.3 Sites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.1.4 Participation and funding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 1.1.5 Public exhibits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 1.1.6 In popular culture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 1.1.7 Associated institutions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 1.1.8 See also . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 1.1.9 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 1.1.10 External links . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Large Hadron Collider . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 1.2.1 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 1.2.2 Purpose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 1.2.3 Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 1.2.4 Operational history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 1.2.5 Findings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 1.2.6 Proposed upgrade . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 1.2.7 Cost . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 1.2.8 Computing resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 1.2.9 Safety of particle collisions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 1.2.10 Operational challenges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 1.2.11 Construction accidents and delays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 1.2.12 Popular culture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 1.2.13 See also . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 1.2.14 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 1.2.15 External links . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 1.2 2 Experiments 23 2.1 List of Large Hadron Collider experiments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 2.1.1 Large Hadron Collider experiments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 2.1.2 See also . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 i ii CONTENTS 2.2 2.3 2.4 2.5 2.1.3 Notes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 2.1.4 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 2.1.5 External links . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 A Large Ion Collider Experiment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 2.2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 2.2.2 History . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 2.2.3 Heavy-Ion Collisions at the LHC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 2.2.4 The ALICE detectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 2.2.5 Data Acquisition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 2.2.6 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 2.2.7 Future Plans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 2.2.8 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 2.2.9 External links . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 ATLAS experiment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 2.3.1 History . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 2.3.2 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 2.3.3 Physics program . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 2.3.4 Micro black holes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 2.3.5 Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 2.3.6 Data systems and analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 2.3.7 See also . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 2.3.8 Notes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 2.3.9 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 2.3.10 External links . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 Compact Muon Solenoid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 2.4.1 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 2.4.2 Physics goals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 2.4.3 Detector summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 2.4.4 CMS by layers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 2.4.5 Collecting and collating the data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 2.4.6 Milestones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 2.4.7 Etymology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 2.4.8 See also . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 2.4.9 Notes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 2.4.10 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 2.4.11 External links . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 VELO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 2.5.1 Physics goals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 2.5.2 The LHCb detector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 2.5.3 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 2.5.4 See also . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 . . . . . .5. . . . . 51 2. . . . . . . . . . .1. . . . . . . . . . .2 3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 TOTEM . . . . 52 Technology 53 3. . . . . . . . . . . . . . . . . . . . . . .2. . . . . . . . . . . 52 2. . . . . . . . . . . . . . . . . . . . . . . . .3 See also . . . . . . . . . . 53 3. . .4. . . . . . . . . . . . . . 57 3.2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 3. . . . . . . . . . . . . . . . . . . . 55 3. . . . . . . . 54 3. . . . . . . . . . . . . . . . . . . . . . 56 3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57 3.2 External links . . . . . 52 2. . 54 LHC@home . . . . . . . . . . . . .7 2. . . . . . . . . . . . . . . . . .1 SixTrack . . . . . . . . . . . . . . . . . . . . . . . . .5 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3. . . 55 3. .3 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4 3. . . . . 52 2. . . . . . . . . . . . . .8. . . . . . . . . . . . . . . . . . . . . .1 Physics goals . . . . . . . . . . . . . . . . . . 51 LHCf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 3. . . . . . 52 2. . . . . . . . . . . .1 See also . . . .2 Description . . . . . . .3. . . .5. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8. . . . 53 LHC Computing Grid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4 See also . . . . . . . . . . . .2. . . . . .2 The LHCb detector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3 External links . . . . . . . . . . . . .CONTENTS 2. . . . . . . . . .6 External links . . . . . . . . . . . . . 55 3. . . . . . . . . .4 External links . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1 Beetle (ASIC) . . . . . . . . . . . . . . . . . . . . . . . . . . . .3. . . . . . . . 52 FP420 experiment . . . . . . . . . . . . . . . . . . . . . . . . . . . .3. . . . . . . . . . . . . . . . . . . . .2 References . . . . . . . . . . .6. . 53 3. . . . . 51 2. 52 2. . . . 53 3. . . . . .5. . . . . . .2 See also . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8. . . . . . .2 External links . . . .2. . . . . . . . . . . . . . . . . . . . . . . . . . 57 3. . . . . . . . . . . . . . . . . . .3 References . . . . . . .1 Background . . . . . . . 52 2.7. . . . . . . . . . . .1 See also . . . . .8 3 2. . . . . . .6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1. . . . . . . . . . . . . . . . . . .5 References . . . . . .5 External links . .2 See also . . . . . . . . . . . . . . . . . . . . . . . . . .2. . . . . . . .5. . . . . . . . . . . . . . . . . . . . . . . . . 51 2. . . . . .4 References . . . . . . . . . . . . . . . . . . .3 Results . . . . . . . . . . . . . . . .6. . . . .3 External links . . . . . . . . . . .5. . . . . . .5. . . . . . . . . . . . . . . . . . . . . . . 57 3. . . 54 3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53 3. . . . . . . . . 56 3. . . . .4. . . . . . . . . . . . . . 55 VELO . . . . . . . . . . . . . . . 56 3. . . . . . . . . . . .5. . . 55 Proton Synchrotron Booster . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7. . . . . . . . . . . . . . . . . . . . . . . . . . . . .6 External links . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 2. . . . . . . . . . . .1 Overview . . .6 2. . . . . . . . . . . . . . .1 See also . . . . . . . . . . .5. . . . . . . . . . . . . 55 3. . . . . . . .1 Purpose . . .5 4 iii Theory 58 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3 3. . . . . . . . . .7. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 Further reading . . . .8 Current status . . 58 4. . . . . . . . . . . .4 Standard Model . . . . . . . . . . . . . . . . . . . . .2. . . 71 4. . 75 4. . . . . . . . . . . . . . . . . . . . . .1 History . . . . . . . . .1. . . . . . . . . .7 Challenges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1. . . . .1. . .1 4. . . . . . . . . . .3 Particle content . . . . . . . . 68 4. . . . . . . . . . . . . . . . . . . . . 63 4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59 4. . . . . . . . . . . . . . . . . . 62 4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75 4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4. . . . . . . . . .1. . . . . . . . . .1. . . . . . . . . . . . . . . . . . . . . 62 4. . . . 68 4. . . . . .3. . .7 Falsifiability . . 59 4. . . .1 Subatomic particles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3 See also . . . . . .2 Overview . . . . . . . . . . . . . . . . . . . . . . . . . .4. . . . . . . . . . . . . . . . . . . . 66 4. .9 Notes and references . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4. . . . . . . . . . .1. . . .4. . . .2 4. . . . . . .8 See also . .6 Supersymmetry in quantum gravity . . . . . . . . . . . . . .12 External links . . . . . . . . . . . . . . . . . . . . . . . . . . . 75 4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 History . . . 67 4. 63 4. . . . . . . . . . . . . . . . . .2. . . . . . . . . . . . . . . . .3. . . . . . . . . . . . . . . . . . . . . . .7 Future . . . .2. . . . . . . . . . . . . . . .5 Supersymmetry as a quantum group . . . . . . . . .5 External links . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70 4. . . .1. . . . . . . . . . .11 Further reading . . . . . . . . . . . . . . . . . . . . . .4 General supersymmetry . . 69 4. . . . . . . . . . . . . . . . . . . . . . . . . . . . .3 Applications 72 4. . . . . . . . . 70 4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9 See also . . 66 4. . . . 70 4. . . . . 59 4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8 See also . . . . . . . .1. . . . . . . . .2 Motivations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4. . . . . . . . . . . . .2. . . . . . . .11 External links . . . . . . . . . . . . . . . . . .2 Recreating superpartners . . . . . . . . . . . . . .1 Theoretical predictions . . .4 References . 76 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4 Theoretical aspects . . . . . . . .2. . . . . . . . . . . . . .3. . . 66 4. . . . . . . . .4. . . . . . . . . . . . .2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3. . . . . . . . . . . . .1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72 4. . . 67 4. . . . . .10 Further reading .1 Historical background . .2. . . . . . . . . . . . . . . . . . . . . . .5 Fundamental forces . . .2. . . . . . . . . . .1. . . . . . . . . . . . .3 4. . . . . . . . . . . . . . .2. . . . . . . . . . 74 4. . . . . . . . .1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4. . . . . . . . . . . . . . . . . . . . 69 4. . . . . . . . . .9 References . . . 70 Superpartner . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65 Particle physics . . . . . . . . . . . . . . . . . . . . . .5 Theory . . . . .4 Experimental laboratories . . . . . . . . . . . . . . . . . . . . . . 63 4. . . 61 4. . . . . . . . . . . . . . .6 Tests and predictions . . . . . . . . . . . . . . .2. . 68 4. . . . . . . . . . 62 4. . . . . 71 4. . 67 4. . . . . . . . . . . 70 Supersymmetry . . . . . .4. . . . . . . . . . . . . . . . . . .3. . . . . . . . . 65 4.6 Practical applications . . . . . . . . . . . .iv CONTENTS 4. . . . . . . . . . . . . . . . . . . . . 70 4. . . . . . . . . . . . . . . . . . . 75 4. . . . . . .3 Standard Model . . . . . . . . . . . . . . .4. . . . . . . . . . . . . . . . . . . . . . . . . . . .2. . . . . . . .1. . . . . . . . . . . . . . . . 70 4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12 Further reading . . . . . . . . . . . . .1. . . . . . . . 114 5.2. . . . 92 4. . . . . . . . . . . . . 79 4. . . . . . . . . . 104 5. . .5. . . . . . . . . 104 5. . . . . . . . . . . . . . . . . . . . .1. . . . . . . . . . . . . . .4. . . . . . . . . . . . . . . . . . . . . . .4.CONTENTS 4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116 5. . . . . . . . . . . . . . . . .1 Theoretical possibility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102 5 Safety 5. . . . . . .2. . . . . . . . . . . . . . . . . . . . . . . .8 Technical aspects and mathematical formulation . . . . . . . . . . . .6 See also . .4. 79 4. . . . . . . . . . . . . .2 Relativistic Heavy Ion Collider . . . . .5. . . . .1 Minimum mass of a black hole . . .2. . . .9 See also . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112 Micro black hole . . . . . . . . . . . . .5. . . . . . . .2. .3 Primordial black holes . . . . . . . . . .11 References . . . . . . . .4. . .2. .2 Significance . . . . . . . . . .2 104 Safety of particle collisions at the Large Hadron Collider . . . . . . . . . . . . . . .1 5. . .13 External links . . . . . . . . . . . . . . . .5. . . . . . . . . . . . . . . . . . . . . . . 82 4. . . . . . 114 5. . . . . . . . . .2. . . . . . . . . . . 109 5. . . . . . . . . . . . . . . . . . . . . . 116 5. . 91 4. . . . . 91 4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5. . . . . . . .10 In Popular Culture . . . . . . .5 Black holes in quantum theories of gravity . . . . . .10 External links . . . .4 See also . . . . . . . . . . . . . . . 80 4. . . . . . . . . . . . . . . . . .5. . . 114 5. . . . . . . . . . . . . . . .4 Manmade micro black holes . . . . . . . . . . . . . . . . . . . . . . . . .2. . . . . . 117 . . . . . . . .5 References . . . . . . . . . . . 76 4. . . . . . . . . . . . 79 Higgs boson . . . . . . . . . . . . . 113 5. 78 4.3 Dangers . . . . 116 5. . .5 v 4. .5.7 Certification of the new particle as a Higgs boson . . . . . . . . . . . . . . . . . . .9 Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . .5. . . . . . . . . . . 112 5. . . . . . . . . . . .2. . . . . . . . . . . . . . . . . . . . . . .1. . . . . 81 4. . . . . . . . . .2 Natural or artificial occurrence . . . . . . . . . . . . .6 External links . . . . . . .8 References .2. . . . . . . . . . . . .6 Public discussion . . . . . . . .1. . . . . . . . . . . . . . . . . . .11 References . . . 114 5. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3. 115 5. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106 5. . . . . . . . .1. . . . . . . . . . . . . . .5. . . . . . . . . . . . .1 A non-technical summary . . . . . . . . . . . .5. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4 Theoretical properties . . . . . . . . . . . . . . . . 88 4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3 History . . . . . . .5. . . . . . . . . . . 116 5. . . . . . . .5 Experimental search . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3 Strangelet . . . . . . . . . . . . . . . . .5. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2. . . . . . . . . . . . .7 Notes . . . . . . . . . . . . . . . . . . . . 113 5. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114 5. . . . . . . . . . . . . . . 76 4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10 Notes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13 External links . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109 5. . . . . . . . . . . . . . . . . . . . . . . 94 4. . . 113 5. 86 4. . . . . . . . . . . . . . . . . . . . . . . . . . . . 102 4. . . .1. . .12 Further reading . . . . . . . . .3. . . . . . . . . . . . . . . . . . . 92 4. . . . . . .3. . . . . . 105 5. . . . .2 Stability of a micro black hole . . . . . .1 Background . . . . . . . . . . . . .3 Large Hadron Collider . . . . . . . . . . . . 118 5. . . . . . .2 References . . . . . . . . . . . . . . .3 External links . . . . . . . . . . .1. . . .2 Images . . . . . .2. . . .2. . . . 129 7. . . . . . . . . . . . . . . . . . . . . . . . . . .1 Injector upgrade . . . . . . 118 5. . . . . . . .1. . . . .3. . . . . . . . 119 Future 6. . . . . . . . . . . . 136 . . . . . . contributors. . . . . . . . . . . . . . . . . . .1 6. . . . . . . . . . . . . . . . . .2 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6 References . . . . . . . . . . . . . . . . . . . . . . . . . . . .3 Content license . . . 120 6. . 120 6. . . . . . . . . . . . . . . . . . . . . . .3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3. . . . . . . . 122 7. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .vi 6 CONTENTS Debate about the strange matter hypothesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118 5. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121 6. . 120 Very Large Hadron Collider . . . . . . . . . . . . . . . . . . . . . . . . .7 Further reading . . . . . . .3 External links . . . . . . . . . . . . . . . . . . . . . . .1 See also . . . . . . . . 120 6. . . . . . . . . . . . . .1 Text . . . . . . .5 In fiction . . . . . . . . . . . . . . . . 121 Text and image sources. . .1. . . . . . . . . . .3. . . . . 120 6. . 120 6. . . . . . .2 7 5. . . . . . . . . . . . . . . . . . .4 120 Super Large Hadron Collider . . . . and licenses 122 7. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2. . . . . . . . . . [1] operated by CERN is commonly referred to as the EuroThe acronym CERN originally stood in French for Con. Established in 1954. council for setting up the laboratory.European governments in 1952. French pronunciation: [sɛʁn]. established by 12 CERN’s main function is to provide the particle accel. see History) is a European research organization that operates the largest particle physics laboratory in the world.23417°N The European Organization for Nuclear Research (French: Organisation européenne pour la recherche nucléaire). known as CERN (/ˈsɜrn/.05278°E 46°14′03″N 6°03′10″E / 46. For the rocket nozzle. Soon after the laboratory’s establishment. apprentices as well as visiting scientists and engineers[4] representing 608 uni.current Organisation Européenne pour la Recherche Nucléaire (European Organization for Nuclear Research) in orations. derived from “Conseil Européen pour la Recherche Nucléaire”. (46°14′3″N 6°3′19″E / 46.1 CERN For the company with the ticker symbol CERN.1 History 1 .Chapter 1 Overview 1. numerous experiments have cil was dissolved. 1954.513 staff members.05528°E) and has 21 European member states. see SERN.Council for Nuclear Research). historically been a major wide area networking hub. even though the name changed to the been constructed at CERN following international collab. it has CERN’s first president was Sir Benjamin Lockspeiser. The first Director General was Edoardo Amaldi. CERN. Israel is the first (and currently only) non-European country granted full The 12 founding member states of CERN in 1954 <sup membership.have become the awkward OERN. the acronym could The main site at Meyrin has a large computer centre con.[3] class="reference plainlinks nourlexpansion” id="ref_[1] "> (map The term CERN is also used to refer to the laboratory. Therefore the laboratory September 1954 by 12 countries in Western Europe. The acronym was reerators and other infrastructure needed for high-energy tained for the new laboratory after the provisional counphysics research – as a result. when the name was changed. the organization is based in the northwest suburbs of Geneva on the Franco–Swiss border. which better de- 1. borders from 1989) which in 2013 counted 2.313 fellows.23417°N 6. which was a provisional versities and research facilities and 113 nationalities. Coordinates: 6. these facilities available to researchers elsewhere.[5] According to Lew Kowarski. see Cerner. because of the need to make is [not]". a former director of CERN is also the birthplace of the World Wide Web. and Heisenberg said taining powerful data processing facilities. its work went beyond the study of the atomic nucleus into higher-energy physics. and hosted some 12. primarily for that the acronym could “still be CERN even if the name experimental-data analysis. associates.1. which is concerned mainly with the study of inThe convention establishing CERN was ratified on 29 teractions between particles.pean laboratory for particle physics (Laboratoire euseil Européen pour la Recherche Nucléaire (European ropéen pour la physique des particules). It also hosts the CERN Internet Exchange Point (CIXP). particle beams before delivering them to experiments or The first website went on-line in 1991. beginning antiprotons electrons neutrinos PS SPS LHC Proton Synchrotron Super Proton Synchrotron Large Hadron Collider Antiproton Decelerator AD n-TOF Neutron Time Of Flight CNGS CERN Neutrinos Gran Sasso CTF3 CLIC TestFacility 3 and Linac3 provides heavy ions at 4. Main article: Faster-than-light neutrino anomaly • 1989: The determination of the number of light neutrino families at the Large Electron–Positron On 22 September 2011. initiated by Tim Berners-Lee in 1989 and Robert Cailliau in 1990.000). to the next more powerful accelerator.” ALICE CMS North Area LHC-b TI8 SPS TT10 Computer science Wide Web See also: History of the World TI2 ATLAS West Area AD CNGS Towards Gran Sasso TT60 TT2 LINAC 2 n-TOF BOOSTER East Area ISOLDE PS CTF3 The World Wide Web began as a CERN project called LINAC 3 ENQUIRE.[9] 2012 it was reported by a new team of scientists for • 2010: The isolation of 38 atoms of antihydrogen.[13] Berners-Lee and Cailliau were jointly honoured by the Association for Computing Machinery in 1995 for their contributions to the develop. They include: ing Grid.incorrectly connected GPS-synchronization cable. in a press release that the results were flawed due to an • 2012: A boson with mass around 125 GeV/c2 con. Linac2 accelerates protons to 50 MeV for inment. A short history of this period can be found at CERN. that the previous experiment was most by scientists of both the • 2011: Maintaining antihydrogen for over 15 likely flawed and will be retested [17] Opera and Icarus teams. the OPERA Collaboration reCollider (LEP) operating on the Z boson peak. protons ions neutrons Prior to the Web’s development. one of the two main internet exchange points in Switzerland. CERN operates a network of six accelerators and a decelBased on the concept of hypertext. traveling apparently faster than light by a • 1999: The discovery of direct CP violation in the factor of 2. jection into the Proton Synchrotron Booster (PSB). is still published on the World • Two linear accelerators generate low energy partiWide Web Consortium's website as a historical docucles.[8] ratory in Italy. in the early 1980s.[10] CERN. • 1973: The discovery of neutral currents in the [6] Gargamelle bubble chamber. CERN had been a pioneer in the introduction of Internet technology.2 CHAPTER 1.2 MeV/u for injection into the Low Energy Ion Ring (LEIR).ch. in March NA48 experiment.2 Particle accelerators The 1984 Nobel Prize in physics was awarded to Carlo Rubbia and Simon van der Meer for the developments Current complex that led to the discoveries of the W and Z bosons.[15] More recently. CERN has become a centre for the development of grid computing. Each machine in the chain increases the energy of at facilitating sharing information among researchers. On 30 April 1993. OVERVIEW scribes the research being performed there. hosting projects including the Several important achievements in particle physics have Enabling Grids for E-sciencE (EGEE) and LHC Computbeen made during experiments at CERN. Faster-than-light neutrino anomaly • 1983: The discovery of W and Z bosons in the UA1 [7] and UA2 experiments.48×10−5 (approximately 1 in 40. in particular the multiwire LHC proportional chamber. Icarus. a statistic with 6. Switzerland to the Gran Sasso National Labothe PS210 experiment.[12] Scientific achievements 1.[19] . Currently active CERN announced that the World Wide Web would be machines are: free to anyone. created by Berners-Lee.1. sent 730 kilometers (450 miles) from CERN near • 1995: The first creation of antihydrogen atoms in Geneva.[16] However. CERN stated [11] minutes. the project was aimed erator. A copy[14] of the original first webpage.0-sigma significance.[18] sistent with long-sought Higgs boson. ported the detection of 17 GeV and 28 GeV muon neutrinos.Map of the CERN accelerator complex ment of the World Wide Web. The 1992 Nobel Prize in physics was awarded to CERN staff researcher Georges Charpak “for his invention and development of particle detectors. on 16 March. it has been used to inject protons and heavy ions into the Large Hadron Collider (LHC).[20] TOTEM.1. Construction of the CMS detector for LHC at CERN The LHC tunnel is located 100 metres underground. It was first commissioned in 1967 and was rebuilt with major upgrades in 1974 and 1992. The radioactive ions are produced by the impact of protons at an energy of 1. • The Low Energy Ion Ring (LEIR) accelerates the ions from the ion linear accelerator. worldwide scientific cooperation project. and with different technologies. Map of the Large Hadron Collider together with the Super Proton Synchrotron at CERN • The Proton Synchrotron Booster increases the energy of particles generated by the proton linear accelerator before they are transferred to the other accelerators. CERN’s existing PS/SPS accelerator complexes will be used to preaccelerate protons which will then be injected into the LHC. and the experiments for it. ATLAS.1. which is used to study unstable nuclei. Construction for these experiments required an extraordinary engineering effort. each of them will study particle collisions from a different point of view. Since 2008. It uses the 27 km circumference circular tunnel previously occupied by LEP which was closed down in November 2000. before transferring them to the Proton Synchrotron (PS). which started operation in 1976. It was designed to deliver an energy of 300 GeV and was gradually upgraded to 450 GeV. and for accelerating high energy electrons and positrons which were injected into the Large Electron–Positron Collider (LEP).4 GeV from the Proton Synchrotron Booster. Large Hadron Collider Collider Main article: Large Hadron Most of the activities at CERN are currently directed towards operating the Large Hadron Collider (LHC). . For example. As well as having its own beamlines for fixed-target experiments (currently COMPASS and NA62). The LHC represents a large-scale. a circular accelerator with a diameter of 2 kilometres built in a tunnel. CERN 3 the velocity of antiprotons to about 10% of the speed of light for research into antimatter. LHC-forward and ALICE) will run on the collider.0–1. a special crane was rented from Belgium to • The Antiproton Decelerator (AD). after having been reconfigured from the previous Low Energy Antiproton Ring (LEAR). • The Super Proton Synchrotron (SPS). This accelerator was commissioned in 2005. LHCb. which studies feasibility issues for the future normal conducting linear collider project. • The Compact Linear Collider Test Facility. MoEDAL. Seven experiments (CMS. which reduces lower pieces of the CMS detector into its underground • The On-Line Isotope Mass Separator (ISOLDE). it has been operated as a proton–antiproton collider (the SppS collider). • The 28 GeV Proton Synchrotron (PS). in the region between the Geneva International Airport and the nearby Jura mountains. built in 1959 and still operating as a feeder to the more powerful SPS. CERN announced that the measurements performed on the newly found particle allowed it to conclude that this is a Higgs boson. but has been extended to span the border since 1965. for all CERN personnel at all times. • B. OVERVIEW cavern. The LHC resumed operation on 20 November 2009 by successfully circulating two beams.000 tons. which assembled the first pieces distributed processing (making use of a specialized grid of true antimatter. and it was stopped for repairs on 19 September 2008. When the 7 TeV experimental period ended. • C. and supera trial successfully streamed 600 MB/s to seven different seded by the Antiproton Decelerator. • The 600 MeV Synchrocyclotron (SC) which started operation in 1957 and was shut down in 1991. for all CERN personnel at specific times. in Switzerland. in Switzerland. There are six entrances to the Meyrin site: • A. and soon began particle collisions at that rate.3 Sites MB/s before 2008. . then scientists must achieve 1. Interior of office building 40 at the Meyrin site. which was originally built in Switzerland alongside the French border. to strengthen the huge magnets inside the accelerator.4 CHAPTER 1. which operated from 1989 to 2000 and was the largest machine of its kind. the LHC Computing Grid). This is like “firing two needles across the Atlantic and getting them to hit each other” according to the LHC’s main engineer Steve Myers. The challenge that the engineers then faced was to try to line up the two beams so that they smashed into each other. sites across the world. since each piece weighed nearly 2. At 1200 BST on 30 March 2010 the LHC successfully smashed two proton particle beams travelling with 3. • The Low Energy Antiproton Ring (LEAR). The smaller accelerators are on the main Meyrin site (also known as the West Area). The initial particle beams were injected into the LHC August 2008.[22] but the system failed because of a faulty magnet connection. CERN scientists announced the discovery of a new sub-atomic particle that could be the much sought after Higgs boson believed to be essential for formation of the Universe. director for accelerators and technology at the Swiss laboratory.[21] The first attempt to circulate a beam through the entire LHC was at 8:28 GMT on 10 September 2008.000 magnets necessary for construction was lowered down a special shaft at 13:00 GMT on 7 March 2005. In July 2012. in 1995.5 TeV (trillion electron volts) of energy.5 trillion electron volts. in Switzerland. this was just the start of the road toward the expected discovery of the Higgs boson. In early 2013 the LHC was shut down for a two-year maintenance period.[23] In March 2013. However. Eventually it will attempt to create 14 TeV events. • The Large Electron–Positron Collider (LEP). comwhich CERN streams to laboratories around the world for missioned in 1982. • The Intersecting Storage Rings (ISR). apart from a line of marker stones. each with an energy of 3. The French side is under Swiss jurisdiction and there is no obvious border within the site. In April 2005. of antihydrogen. The first of the approximately 5. resulting in a 7 TeV event.[24] Decommissioned accelerators • The original linear accelerator (LINAC 1). for all CERN personnel at specific times.800 1.1. consisting of nine atoms infrastructure. the LHC revved up to 8 TeV (4 TeV acceleration in both directions) in March 2012. Building 40 hosts many offices for scientists from the CMS and ATLAS collaborations. If all the data generated by the LHC is to be analysed. housed in a 27 km-long circular tunnel which now houses the Large Hadron Collider. It was closed in 1996. The LHC has begun to generate vast quantities of data. an early collider built from 1966 to 1971 and operated until 1984. Often referred to as the main entrance. most are officially named and numbered after the site where they were located. no taxes are payable when such transfers are made. All new members have remained in the organization continuously since their accession. The largest of the experimental sites is the Prévessin site.[24] CERN’s main site. The experiments are located at the same underground level as the tunnels at these sites. UA2 and the LEP experiments (the latter which will be used for LHC experiments). such as Richard Feynman. situated underground at sites on the SPS accelerator.[27] As of 2014. Switzerland and Norway are not. Other sites are the ones which were used for the UA1. NA32 was an experiment looking at the production of charmed particles and located at the Prévessin (North Area) site while WA22 used the Big European Bubble Chamber (BEBC) at the Meyrin (West Area) site to examine neutrino interactions. and rejoined in 1983. the contribution per person in 2014 is about 2. except Spain and Yugoslavia.2 CHF/year. and are mostly buried under French farmland and invisible from the surface. Of the twenty members. • E. This is the only permitted route for such transfers.[25] Member states and budget • Inter-site tunnel. and Albert Einstein.1. with ATLAS in Switzerland. Israel joined CERN as a full member on 6 January 2014. times. in France. CERN 5 • D. The UA1 and UA2 experiments were considered to be in the Underground Area. Averaged across those states. in France. from Switzerland looking towards France The SPS and LEP/LHC tunnels are almost entirely outside the main site. i. Controlled by customs personnel.[31] . 18 are European Union member states. in Switzerland. Three of these experimental sites are in France. CERN regularly accepted new members. However. withdrew in 1969.e.1.1. for French-resident CERN personnel at specific times. although some of the ancillary cryogenic and access sites are in Switzerland. for equipment transfer to and from CERN sites in France by personnel with a specific permit.[29][30] [3] Acceded members became CERN member states upon signing an accession agreement. Spain first joined CERN in 1961.[24] 1. for goods reception at specific famous physicists. Yugoslavia was a founding member of CERN but left in 1961. CERN receives contributions from states with a total population of about 517 million people.[31] [4] Additional contribution from Candidates for Accession and Associate Member States. Most of the roads on the CERN campus are named after Member states of CERN and current enlargement agenda CERN members Accession in progress Declared intent to join Since its foundation by 12 members in 1954. either as the location of buildings associated with experiments or other facilities needed to operate the colliders such as cryogenic plants and access shafts. Initially only West Germany was a (founding) member of CERN.[28] [2] 12 founding members drafted the Convention for the Establishment of a European Organization for Nuclear Research which entered into force on 29 September 1954. For example. which is the target station for noncollider experiments on the SPS accelerator. Under the CERN treaty. Niels Bohr. [1] Based on the population in 2014. they have surface sites at various points around them. also known as the North Area.[26] becoming the first (and currently only) non-European member. Outside of the LEP and LHC experiments. Controlled by customs personnel.4 Participation and funding Named “Porte Charles de Gaulle” in recognition of his role in the creation of CERN. first approved by CERN Council in December 2008.[36] Turkey Scientific contacts: 19 c. which cooperates scientifically with CERN since 1991.[33] • Cyprus became an associate member on 5 October 2012.[41] became a candidate for accession to CERN on 11 February 2010[32] and will become a full member in 2015.[34] • Ukraine became an associate member on 3 October 2013.[49] Turkey – from 1961 to 2014 Turkey became associate member and will become full member in 2016 • Russia – since 1993 • Japan – since 1995 • United States – since 1997 • India – since 2002 Also observers are the following international organizations: • UNESCO – since 1954 • European Commission – since 1985 . • Pakistan became an associate member on 19 Four countries have observer status:[50] June 2014. not of ratification): • Romania.[37] • More countries have confirmed their wish to become members and are awaiting approval from the CERN Council:[47] • • + Slovenia. Cyprus. Declared intent to join: 2 c.[42] • Serbia became a candidate for accession to CERN on 19 December 2011. Observers: 4 c. Slovenia. formally applied for membership in 2012. applied for membership in 2009. Brazil still needs to sign and ratify its accession agreement. May 2014. OVERVIEW Enlargement International relations Associate Members.[35] • Brazil was approved by CERN Council on 13 December 2013[45] to become the first Latin American associate member.[48] Russia. working with CERN in practice since 1959 (as the former Soviet Union) and currently an observer state. As of July 2014. Candidates (note that dates are initial signature. signed an association agreement on 10 January 2012[43][44] and became an official “Associate Member in the pre-stage to Membership” on 15 March 2012.6 CHAPTER 1. Accession in progress: 3 c.[46] CERN member states: 21 c. + EU • Turkey became an associate member on 12 Cooperation agreement: 35 c. CERN 7 Non-Member States (with dates of Co-operation Agreements) currently involved in CERN programmes are: • Algeria • Argentina – 11 March 1992 • Armenia – 25 March 1994 • Australia – 1 November 1991 • Azerbaijan – 3 December 1997 • Belarus – 28 June 1994 • Bolivia • Brazil – 19 February 1990 & October 2006 • Canada – 11 October 1996 • Chile – 10 October 1991 • • Romania – 1 October 1991. Since 12 December 2008 it has the Status of Candidate for Accession to Membership.[52] Lithuania – 9 November 2004 • Macedonia – 27 April 2009 • Malta – 10 January 2008[54][55] • Thailand • Mexico – 20 February 1998 • Tunisia • Montenegro – 12 October 1990 • Uzbekistan • Morocco – 14 April 1997 • Venezuela • New Zealand – 4 December 2003 • Peru – 23 February 1993 [53] International research institutions.[57] . MoU with Jordan and SESAME.1. • Ukraine – 2 April 1993 • United Arab Emirates – 18 January 2006 • Vietnam CERN also has scientific contacts with the following countries:[56] China – 12 July 1991.12 June 2003. 14 August 1997 & 17 February 2004 • Cuba • Ghana • Ireland • Latvia • Lebanon • Madagascar • Malaysia • Mozambique • Palestinian Authority • Colombia – 15 May 1993 • Croatia – 18 July 1991 • Cyprus – 14 February 2006 • Ecuador • Egypt – 16 January 2006 • Estonia – 23 April 1996 • Georgia – 11 October 1996 • Iceland – 11 September 1996 • Philippines • Iran – 5 July 2001 • Qatar • Rwanda • Singapore • Sri Lanka • Taiwan • • [51] Jordan . • Saudi Arabia – 21 January 2006 • Slovenia – 7 January 1991 • South Africa – 4 July 1992 • South Korea – 25 October 2006. such as CERN. can aid in science diplomacy. in preparation of a cooperation agreement signed in 2004.1. a self-proclaimed time traveler. • CERN is depicted in the visual novel/anime series Steins.1.[58][59][60] Switzerland” and steals a “superconducting bending magnet created for use in tests with particle acceleration” to use in his son Stan’s Pinewood Derby 1. • The Microcosm museum on particle physics and CERN history. line 18 goes to CERN • CERN’s Large Hadron Collider is the subject of a (scientifically accurate) rap video starring Katherine McAlpine with some of the facility’s staff. dance of Chidambaram. The break-in is captured on surveillance tape which is then broadcast on the news.5 Public exhibits Facilities at CERN open to the public include: • The Globe of Science and Innovation. a shadowy organization that has been researching time travel in order to restructure and control the world. the father of one of the main characters. Episode 6) called “Pinewood Derby”. Shiva.8 CHAPTER 1. OVERVIEW The Globe of Science and Innovation at CERN 1.[64] • In the popular children’s series The 39 Clues.Gate as SERN. CERN is explored throughout the inside. parallelling the movements or “dance” of subatomic particles. alleged that CERN would invent time travel in 2001. • The Hindu deity.6 In popular culture racer. and depicts the events surrounding the discovery of the Higgs Boson in 2013 • In Dan Brown's mystery-thriller novel Angels & Demons. a canister of antimatter is stolen from CERN. Randy breaks into CERN dressed in disguise as Princess Leia from the Star Wars saga. breaks into the “Hadron Particle Super Collider in • In a documentary entitled Particle Fever. which opened in late 2005 and is used four times a week for special exhibits.[61][62] • CERN is depicted in an episode of South Park (Season 13. Randy Marsh.1. a 2-metre statue styled on The statue of Shiva engaging in the Nataraja dance presented by Chola bronzes of the deity engaging in the Nataraja the Department of Atomic Energy of India.[63] • John Titor. . CERN is said to be an Ekaterina stronghold hiding the clue hydrogen. “MoEDAL becomes the LHC’s magnificent seventh”. CNN. Physics Letters B 465: 335. • The 2012 student film Decay. 30 September 2011. CERN.cern. The Times Of India. Press. 7 August 2008”.home.ch”. Neutrinos Travel Faster Than Light. • In season 3 episode 15 of the popular TV sitcom The Big Bang Theory titled “The Large Hadron Collision”.ch”. [14] “W3. [2] “CERN – Council Delegates”.ch”.335F. Retrieved 20 November 2010. Public. “A new measurement of direct CP violation in two pion decays of the neutral kaon”. Public. Retrieved 16 August 2012.web. Retrieved on 2013-0717. [22] “CERN press release.ch”. Sawyer's science fiction novel Flashforward.ch”. Retrieved 20 November 2010.ch. Press. CERN. (1998). the main character is scouted by “CERM” [11] Jonathan Amos [6 June 2011]BBC © 2011 Retrieved 2011-06-06 • In Super Lovers.web.cern. The Associated Press. Retrieved 20 November 2010. W3. Haruko (Ren’s mother) worked at CERN.[65] 9 [4] “CERN Annual Report 2013 – CERN in Figures”. [17] The Associated Press.ch (2012-07-04). and Ren was taught by CERN professors [12] CERN experiments observe particle consistent with long-sought Higgs boson | CERN press office. [7] “CERN.ch. [66] 1.ch. Retrieved 20 November 2010.cern.cern. 22 September 2011.ch.1.ch. 5 May 2010 [21] Overbye. the Large Hadron Collider accelerator is performing a run to search for the Higgs boson when the entire human race sees themselves twenty-one years and six months in the future. Press.8 See also • CERN Openlab • Fermilab • Nederlandse Organisatie voor Wetenschappelijk Onderzoek • Science and technology in Switzerland • Scientific Linux • SLAC National Accelerator Laboratory • World Wide Web • Large Hadron Collider – Wikipedia book 1.ch.9 References [1] “CERN. arXiv:hep-ex/9909022.. at CERN. CERN • In Robert J. [3] The boycott movement is losing the battle – for now [13] “CERN.ch. Retrieved 20 November 2010.1. which centers around the idea of the Large Hadron Collider transforming people into zombies. CERN scientists say”. Retrieved 4 September 2014. (The Rap Is Already Written.)". • The Compact Muon Solenoid at CERN was used as the basis for the Megadeth's Super Collider album cover. [15] “CERN. [16] Adrian Cho. . Retrieved 20 [8] “CERN. The New York Times. 7 August 2008. “Einstein Proved Right in Retest of Neutrinos’ Speed”.ch La”. [20] CERN Courier. could be the Higgs boson. cern.ch. [10] “Antihydrogen isolation”.cern. 17 March 2012. November 2010. [6] “CERN.ch. According to One Experiment.ch. • CERN forms part of the back story of the massively multiplayer augmented reality game Ingress. "Let the Proton Smashing Begin.1. [5] “The Name CERN”.web. [19] “CERN Website – LINAC”. Retrieved 4 July 2012. Retrieved 20 November 2010. V.1.cern. was filmed on location in CERN’s maintenance tunnels. • In Denpa Kyoushi.cern. 18 November 2010.org.web. CERN.465. [18] “CERN Press Release”..org”. et al.cern. Bibcode:1999PhLB.cern. Science NOW.1. [9] Fanti. Retrieved 20 November 2010. [24] “New results indicate that particle discovered at CERN is a Higgs boson”.1016/S03702693(99)01030-8.web.7 Associated institutions • Swiss National Supercomputing Centre 1. doi:10. Public. Leonard and Rajesh travel to CERN to attend a conference and see the LHC. CERN press release. Dennis (29 July 2008). Retrieved 4 September 2014. 4 July 2012. Public. Retrieved 20 November 2010. Public.web.web. Linac2. [23] "'God particle': New particle found.web. Mia. CERN website. Retrieved 5 July 2014. European Space Agency. 13 December 2013. CERN Council website. CERN Bulletin. 3 April 2013. swissinfo. Nirmala (2000). (2013-11-11) Israel may become first non-European member of nuclear research group CERN – Diplomacy and Defense Israel News.com. [43] “Vesti – Srbija zvanično postala član CERN-a”. 31 March 2010. Retrieved 31 January 2012. Government of Pakistan press releases. [37] “Pakistan Becomes the First Associate CERN Member from Asia”. 17 October 2011.. CERN press release.estadao. Retrieved 16 July 2012. Science & Diplomacy 2 (3). Times of Malta.cern. CERN. Retrieved 5 July 2014. [30] “CONVENTION FOR THE ESTABLISHMENT OF A EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCH”. ISBN 978-955-8156-43-8.1038/nature09610. doi:10. [57] Quevedo. [59] Ramachandran. [63] “Southparkstudios. 3 October 2013. Retrieved 4 July 2012. [44] “Serbia expected to become CERN Associate Member”. ISBN 92-9092-397-0.ch. OVERVIEW [25] <Please add first missing authors to populate metadata. [31] “CERN Member States”.673A. Retrieved 23 May 2014. 673–6. Retrieved 5 July 2014. B. 5 October 2012. 11 January 2008. CERN press release. 24 June 2011.com. 41– 42. CERN. [40] “Observers”. Retrieved 5 July 2014. Retrieved 20 November 2010. Retrieved 5 July 2014. [62] “Large Hadron Collider Rap Video Is a Hit”. [35] “Ukraine to become Associate Member State of CERN”.). [49] “Russia officially joins CERN at last”. [51] “CERN International Relations – Jordan”. [64] “Angels and Demons”. [46] “Brasil fará parte do maior laboratório de física do Mundo”. [54] “Prime Minister of Malta visits CERN”.com”. Retrieved 5 July 2014. Retrieved 23 May 2014. [58] “Shiva’s Cosmic Dance at CERN”. Retrieved 7 December 2011. [36] “Turkey to become Associate Member State of CERN”. [55] “Malta signs agreement with CERN”. [47] “24 June 2011: CERN – CERN Council looks forward to summer conferences and new members”. G. et al. Nature 468 (7324): Bibcode:2010Natur. (2010).br. 10 January 2008. pp.10 CHAPTER 1. CMS Experiment web site. 2000–2002. 29 November 2013. CERN Courier. Fritjof Capra. CERN. CERN. Pannipitiya : Stamford Lake Publication. 10 September 2008. 1 October 2013. Retrieved 21 December 2013. CERN Council website. [45] “Decisions from CERN Council’s 169th session”. [52] “CERN International Relations – SESAME”. [33] “CERN Associate Members”. CERN. South Park Studios. 20 June 2014. . [41] “CERN International Relations – Romania”. Retrieved 5 July 2014. Government of Pakistan. Fazlur. 16 March 2012. [60] Smith. Fernando (July 2013). Retrieved 5 July 2014. CERN Council website. Retrieved 5 July 2014. Retrieved 4 July 2012. Youtube.ch. [61] “Youtube. Retrieved 14 December 2009. Retrieved 20 November 2010. [34] “The Republic of Cyprus becomes a CERN Associate Member State”. PMID 21085118. Ministry of Foreign Affairs. CERN. CERN.web. Retrieved 16 July 2012. Retrieved 5 July 2014. 18 June 2004. CERN. [50] “ISAAR relationship data at CERN library”. ISBN 9780-521-52865-8. “Trapped antihydrogen”. Retrieved 16 July 2012. Hindu heritage. National Geographic News. [27] Rahman. 18 January 2012. CERN. Retrieved 4 July 2012. Retrieved 6 July 2014. CERN. [26] “CERN Internationl Relations – Israel”. CERN. 12 May 2014.org. Retrieved 6 July 2014. Retrieved 5 July 2014. www. Retrieved 7 December 2011. Retrieved 25 May 2011. 13 December 2013. “Red Carpet for CERN’s 50th”.web. “The Importance of International Research Institutions for Science Diplomacy”. David.468. The Dance of Siva: Religion. 24 January 2014. Retrieved on 2014-04-28.mk.com”. [38] “Member States’ Contributions – 2014”. CERN. Haaretz. CERN. September 2005. CERN.cern. Internationalrelations. Retrieved 5 July 2014.ch. [28] List of countries by population [29] ESA Convention (6th ed. [56] “Member states”. International-relations. CERN press release. CERN. CERN bulletin. B92. [39] “Final Budget of the Organization for the sixtieth financial year 2014”. Retrieved 13 August 2010. [32] “Romania takes first steps to join CERN”. [42] Andresen. Interactions. Cambridge University Press. Art and Poetry in South India.> (November 2004). Retrieved 23 May 2014. [53] "''Macedonia joins CERN (SUP)''". [48] “CERN International Relations – Slovenia”. as well as hundreds of universities and laboratories. The LHC is expected to address some to 6. The LHC matching the Higgs boson was confirmed by data from went into shutdown for upgrades to increase beam energy the LHC in 2013. μ+ μ− ). to be analysed by a grid2008. Retrieved 22 November 2012. with reopening currently planned of the unsolved questions of physics. 1. advancing human A section of the LHC .000 scientists and engineers from over 100 countries. As of 2014.2.[18] and the LHC began its planned research program. and particularly prove [20] Proton–proton collisions are the [2] and at 4 TeV in 2012. or lead nuclei (574 TeV per nucleus. [66] /2014/01/a-year-of-google-ingress/ 1. The LHC has discovered a massive 125 GeV boson (which subsequent results confirmed to be the long-sought Higgs boson) and several composite particles (hadrons) largest and most powerful particle collider.64 microjoules). The incident resulted in damage to over 50 superconducting magnets and their mountings. see LHC (disam. 2010. causing both a magnet quench and several tons of helium gas escaping with explosive force.[12] but nine days later a faulty electrical connection led to the rupture of a liquid helium enclosure. September of tens of petabytes per year. and the largest like the χ (3P) bottomonium state. It contains seven detectors. or 2. Rebecca (31 October 2012). and contamination of the vacuum pipe. or disprove the existence of the theorized Higgs boson main operation mode. beams successfully circulated in the main ring of the LHC The Large Hadron Collider (LHC) is the world’s for the first time. For other uses. 2011 and 2013.2 Large Hadron Collider comprising over 170 computing facilities in a worldwide network across 36 countries[9][10][11] ). A BBC Radio program based computer network infrastructure connecting 140 computing centers in 35 countries[7][8] (by 2012 the LHC Computing Grid was the world’s largest computing grid.[3] The discovery of a particle about one month each in 2010.1.[1] built by the European Orgluon plasma. which challenged the validity of existing models Its aim is to allow physicists to test the predictions of of supersymmetry. 2009 proton beams were successfully circulated again.10 External links • Official website of CERN: CERN Accelerating science 11 understanding of physical laws.[15][16] with the first recorded proton– proton collisions occurring three days later at the injection energy of 450 GeV per beam.ther protons at up to 4 teraelectronvolts (4 TeV or 0. Switzerland. Collision data was also anticipated to be produced at an unprecedented rate • Big Bang Day: The Making of CERN. It is also the longest machine ever built.5 TeV beams. “Large Hadron Collider Unleashes Rampaging Zombies”.1. setting a world record for the highest-energy man-made particle collisions.5 TeV (13 TeV collision energy) —about seven nuclear research group CERN times the previous record— in 2015.[17] On March 30. with proton biguation). The LHC was built in collaboration with over 10. each designed for certain kinds of research.5 TeV per beam. LARGE HADRON COLLIDER [65] Boyle. created a quark– single machine in the world.[19] different theories of particle physics and high-energy The LHC operated at 3. and recorded the first observations of the ganization for Nuclear Research (CERN) from 1998 to very rare decay of the B meson into two muons (B 0 → 2008.76 energy physics TeV per nucleon). the LHC remains the largest and most complex experimental facility ever built. Its synchrotron is • CERN at 50 designed to collide two opposing particle beams of ei• CERN Courier – International journal of high.[5][6] with energies to be increased to • Israel may become first non-European member of around 6. the first collisions took place between two 3. as deep as 175 metres (574 ft) beneath the Franco-Swiss border near Geneva.[4] It lies in a tunnel 27 kilometres (17 mi) in circumference. and delayed further operations by 14 months.The LHC went live on 10 September 2008. “LHC” redirects here. It collided protons with lead nuclei and of the large family of new particles predicted by for two months in 2013 and used lead–lead collisions for supersymmetric theories.5 TeV per beam in 2010 and 2011 physics like the Standard Model.[13][14] On November 20. believed to have existed in the early universe the elementary objects. The best-known hadrons are the baryons protons and neutrons.2.[26][27][28] duced at the LHC. realized in The LHC is the world’s largest and highest-energy particle nature. Data is also needed from high energy particle experiments to suggest which versions of current scientific mod. dicted by various Grand Unification Theories. Thus many of them are hard or near impossible to study in • Are there additional sources of quark flavour other ways. and can we detect them?[33] • What is the nature of the dark matter that appears to account for 27% of the mass-energy of the universe? The term hadron refers to composite particles composed of quarks held together by the strong force (as atoms Other open questions that may be explored using high enand molecules are held together by the electromagnetic ergy particle collisions: force). The A collider is a type of a particle accelerator with two diLHC may clarify whether the electroweak force and rected beams of particles.2. which were discovered during cosmic ray weak nuclear force are different manifestations of experiments in the late 1940s and early 1950s. Many of these three fundamental forces? See also Hierarchy probbyproducts are produced only by high energy collisions. implying that all known particles have accelerator. Z H • Are the masses of elementary particles actually generated by the Higgs mechanism via electroweak symmetry breaking?[25] It is expected that the collider will either demonstrate or rule out the existence of the elusive Higgs boson. thereby allowing physicists to consider whether the Standard Model or its Higgsless alternatives are more likely to be A Feynman diagram of one way the Higgs boson may be procorrect. OVERVIEW for mid-March 2015.3 Design els are more likely to be correct – in particular to choose between the Standard Model and Higgsless models and to validate their predictions and allow further theoretical development. Z which combine to make a neutral Higgs. and they decay after very short periods of time. as prehigh kinetic energies and let them impact other particles. the deep structure of space and and in certain compact and strange astronomical obtime. lem. q W. • Is supersymmetry. Physicists hope that the LHC will help answer some of the fundamental open questions in physics. where current theories collisions.[5][34] The collider is contained in a circular supersymmetric partners?[29][30][31] tunnel.12 CHAPTER 1.1. a single force called the electroweak force. as the Standard Model appears to be unsatisfactory. an extension of the Standard Model and Poincaré symmetry.[21][22] 1.1 Background • Are there extra dimensions. mainly in ALICE. two quarks each emit a W or Z boson. at .2 Purpose • Why are there apparent violations of the symmetry between matter and antimatter? See also CP violation. and in particular the interrelation between quantum jects today? This will be investigated by heavy ion mechanics and general relativity. beyond those already present within the Standard Model? 1. concerning the • What are the nature and properties of quark–gluon basic laws governing the interactions and forces among plasma.[32] as predicted by various models based on string theory. mixing. hadrons also include mesons such as the • It is already known that electromagnetism and the pion and kaon. with a circumference of 27 kilometres (17 mi).2. Here. Many theorists expect new physics beyond the Standard Model to emerge at the TeV energy level. and knowledge are unclear or break down altogether. Analysis of the byproducts of these collisions gives sci• Why is the fourth fundamental force (gravity) so entists good evidence of the structure of the subatomic many orders of magnitude weaker than the other world and the laws of nature governing it. In particle physics colliders are the strong nuclear force are similarly just different used as a research tool: they accelerate particles to very manifestations of one universal unified force. Issues 0 possibly to be explored by LHC collisions include:[23][24] q W. 1. which feeds the Proton Synchrotron Booster (PSB). with 115 billion protons in each bunch so that interactions between the two beams will take place at discrete intervals never shorter than 25 nanoseconds (ns) apart. ventilation equipment. once or twice a day.[40] The 3. When running at full design power of 7 TeV per beam.[39] The design luminosity of the LHC is 1034 cm−2 s−1 . into up to 2.500 and move at about 0.9 K (−271. The 2-in-1 structure of the LHC dipole magnets a depth ranging from 50 to 175 metres (164 to 574 ft) underground.[38] It will take less than 90 microseconds (μs) for a proton to travel once around the main ring – a speed of about 11. accelerated (over a period of 20 minutes) to tal. their peak energy. erated to 26 GeV. LARGE HADRON COLLIDER 13 with most weighing over 27 tonnes. over 1. where the two beams cross. at their operating temperature of 1. as the protons are accelerated from 450 GeV to 7 TeV. was formerly used to house the Large Electron–Positron Collider. which travel in opposite There the protons are accelerated to 1. ticles are prepared by a series of systems that succescontrol electronics and refrigeration plants. and finally circulated for 5 to 24 hours .3 teslas (T). providing a bunch collision rate of 40 MHz. tons. The first system is the linear The collider tunnel contains two adjacent parallel particle accelerator LINAC 2 generating 50-MeV probeamlines (or beam pipes) that intersect at four points.232 dipole magnets into the Proton Synchrotron (PS). giving a total collision energy of 14 TeV. with most of it in France.25 °C).[35] It crosses the border between Switzerland and France at four points. Rather than continuous beams. Some 1.8-metre (12 ft) wide concrete-lined tunnel.4 GeV and injected directions around the ring. or about 3 metres per second slower than the speed of light (c). each containing a proton beam. In to.600 superconducting magnets are installed. Here the proton bunches are intersection points.54 to 8.808 bunches.accumulated. However it will be operated with fewer bunches when it is first commissioned.[37] Approximately 96 tonnes of superfluid helium 4 is needed to keep the magnets. At this energy the protons have a Lorentz factor of about 7. Map of the Large Hadron Collider at CERN Superconducting quadrupole electromagnets are used to direct the beams to four intersection points. making the LHC the largest cryogenic facility in the world at liquid helium temperature.000 revolutions per second. constructed between 1983 and 1988.999999991 c. where interactions between accelerated protons will take place. sively increase their energy.2. the parequipment such as compressors. the protons will be bunched together. the field of the superconducting dipole magnets will be increased from 0. The protons will each have an energy of 7 TeV. Finally the Super Proton Synchrotron while an additional 392 quadrupole magnets are used (SPS) is used to further increase their energy to 450 GeV to keep the beams focused. in order to maximize the before they are at last injected (over a period of several chances of interaction between the particles in the four minutes) into the main ring. Surface buildings hold ancillary Prior to being injected into the main accelerator. made of copper-clad niobium-titanium. giving it a bunch crossing interval of 75 ns. where they are accelkeep the beams on their circular path (see image[36] ). 14 while collisions occur at the four intersection points.[41] CHAPTER 1. OVERVIEW Computing and analysis facilities Main article: LHC Computing Grid The LHC Computing Grid is an international collaborative project that consists of a grid-based computer network infrastructure initially connecting 140 computing centers in 35 countries (over 170 in 36 countries as of 2012). It was designed by CERN to handle the significant volume of data produced by LHC experiments.[7][8] By 2012 data from over 6 quadrillion (6 x 1015 ) LHC proton-proton collisions had been analyzed,[44] LHC collision data was being produced at approximately 25 petabytes per year, and the LHC Computing Grid had become the world’s largest computing grid (as of 2012), comprising over 170 computing facilities in a worldwide network across 36 countries.[9][10][11] 1.2.4 Operational history Inaugural tests CMS detector for LHC The first beam was circulated through the collider on the morning of 10 September 2008.[43] CERN successfully fired the protons around the tunnel in stages, three kilometres at a time. The particles were fired in a clockwise direction into the accelerator and successfully steered around it at 10:28 local time.[45] The LHC successfully completed its major test: after a series of trial runs, two white dots flashed on a computer screen showing the protons travelled the full length of the collider. It took less than one hour to guide the stream of particles around its inaugural circuit.[46] CERN next successfully sent a beam of protons in a counterclockwise direction, taking slightly longer at one and a half hours due to a problem with the cryogenics, with the full circuit being completed at 14:59. The LHC physics program is mainly based on proton– proton collisions. However, shorter running periods, typically one month per year, with heavy-ion collisions are included in the program. While lighter ions are considered as well, the baseline scheme deals with lead ions[42] (see A Large Ion Collider Experiment). The lead ions are first accelerated by the linear accelerator LINAC 3, and the Low-Energy Ion Ring (LEIR) is used as an ion storage and cooler unit. The ions are then further accelerated by the PS and SPS before being injected into LHC ring, where they reached an energy of 1.58 TeV per nucleon (or 328 TeV per ion), higher than the energies reached 2008 quench incident by the Relativistic Heavy Ion Collider. The aim of the heavy-ion program is to investigate quark–gluon plasma, On 19 September 2008, a magnet quench occurred in about 100 bending magnets in sectors 3 and 4, where which existed in the early universe. an electrical fault led to a loss of approximately six tonnes of liquid helium (the magnets’ cryogenic coolant), Detectors which was vented into the tunnel. The escaping vapor expanded with explosive force, damaging over 50 See also: List of Large Hadron Collider experiments superconducting magnets and their mountings, and contaminating the vacuum pipe, which also lost vacuum [13][14][47] Seven detectors have been constructed at the LHC, lo- conditions. cated underground in large caverns excavated at the LHC’s intersection points. Two of them, the ATLAS experiment and the Compact Muon Solenoid (CMS), are large, general purpose particle detectors.[34] ALICE and LHCb have more specific roles and the last three, TOTEM, MoEDAL and LHCf, are very much smaller and are for very specialized research. The BBC’s summary of the main detectors is:[43] Shortly after the incident CERN reported that the most likely cause of the problem was a faulty electrical connection between two magnets, and that – due to the time needed to warm up the affected sectors and then cool them back down to operating temperature – it would take at least two months to fix.[48] CERN released an interim technical report[47] and preliminary analysis of the incident on 15 and 16 October 2008 respectively,[49] and a 1.2. LARGE HADRON COLLIDER more detailed report on 5 December 2008.[50] The analysis of the incident by CERN confirmed that an electrical fault had indeed been the cause. The faulty electrical connection had led (correctly) to a failsafe power abort of the electrical systems powering the superconducting magnets, but had also caused an electric arc (or discharge) which damaged the integrity of the supercooled helium’s enclosure and vacuum insulation, causing the coolant’s temperature and pressure to rapidly rise beyond the ability of the safety systems to contain it,[47] and leading to a temperature rise of about 100 degrees Celsius in some of the affected magnets. Energy stored in the superconducting magnets and electrical noise induced in other quench detectors also played a role in the rapid heating. Around two tonnes of liquid helium escaped explosively before detectors triggered an emergency stop, and a further four tonnes leaked at lower pressure in the aftermath.[47] A total of 53 magnets were damaged in the incident and were repaired or replaced during the winter shutdown.[51] In the original timeline of the LHC commissioning, the first “modest” high-energy collisions at a center-of-mass energy of 900 GeV were expected to take place before the end of September 2008, and the LHC was expected to be operating at 10 TeV by the end of 2008.[52] However, due to the delay caused by the above-mentioned incident, the collider was not operational until November 2009.[53] Despite the delay, LHC was officially inaugurated on 21 October 2008, in the presence of political leaders, science ministers from CERN’s 20 Member States, CERN officials, and members of the worldwide scientific community.[54] Most of 2009 was spent on repairs and reviews from the damage caused by the quench incident, along with two further vacuum leaks identified in July 2009 which pushed the start of operations to November of that year.[55] Full operation On 20 November 2009, low-energy beams circulated in the tunnel for the first time since the incident, and shortly after, on 30 November, the LHC achieved 1.18 TeV per beam to become the world’s highest-energy particle accelerator, beating the Tevatron's previous record of 0.98 TeV per beam held for eight years.[56] The early part of 2010 saw the continued ramp-up of beam in energies and early physics experiments towards 3.5 TeV per beam and on 30 March 2010, LHC set a new record for high-energy collisions by colliding proton beams at a combined energy level of 7 TeV. The attempt was the third that day, after two unsuccessful attempts in which the protons had to be “dumped” from the collider and new beams had to be injected.[57] This also marked the start of its main research program. 15 6 December 2010,[58] allowing the ALICE experiment to study matter under extreme conditions similar to those shortly after the Big Bang.[59] CERN originally planned that the LHC would run through to the end of 2012, with a short break at the end of 2011 to allow for an increase in beam energy from 3.5 to 4 TeV per beam.[20] At the end of 2012 the LHC would be shut down until around 2015 to allow upgrade to a planned beam energy of 7 TeV per beam.[21] In late 2012, in light of the July 2012 discovery of a new particle, the shutdown was postponed for some weeks into early 2013, to allow additional data to be obtained prior to shutdown. Timeline of operations 1.2.5 Findings CERN scientists estimated that, if the Standard Model is correct, several Higgs bosons would be produced every minute, and that over a few years enough data to confirm or disprove the Higgs boson unambiguously and to obtain sufficient results concerning supersymmetric particles would be gathered to draw meaningful conclusions.[5] Some extensions of the Standard Model predict additional particles, such as the heavy W' and Z' gauge bosons, which may also lie within reach of the LHC to discover.[74] The first physics results from the LHC, involving 284 collisions which took place in the ALICE detector, were reported on 15 December 2009.[61] The results of the first proton–proton collisions at energies higher than Fermilab’s Tevatron proton–antiproton collisions were published by the CMS collaboration in early February 2010, yielding greater-than-predicted charged-hadron production.[62] After the first year of data collection, the LHC experimental collaborations started to release their preliminary results concerning searches for new physics beyond the Standard Model in proton-proton collisions.[75][76][77][78] No evidence of new particles was detected in the 2010 data. As a result, bounds were set on the allowed parameter space of various extensions of the Standard Model, such as models with large extra dimensions, constrained versions of the Minimal Supersymmetric Standard Model, and others.[79][80][81] On 24 May 2011, it was reported that quark–gluon plasma (the densest matter besides black holes) has been created in the LHC.[66] Between July and August 2011, results of searches for the Higgs boson and for exotic particles, based on the data collected during the first half of the 2011 run, were presented in conferences in Grenoble[82] and Mumbai.[83] In The first proton run ended on 4 November 2010. A run the latter conference it was reported that, despite hints with lead ions started on 8 November 2010, and ended on of a Higgs signal in earlier data, ATLAS and CMS ex- 16 clude with 95% confidence level (using the CLs method) the existence of a Higgs boson with the properties predicted by the Standard Model over most of the mass region between 145 and 466 GeV.[84] The searches for new particles did not yield signals either, allowing to further constrain the parameter space of various extensions of the Standard Model, including its supersymmetric extensions.[85][86] On 13 December 2011, CERN reported that the Standard Model Higgs boson, if it exists, is most likely to have a mass constrained to the range 115–130 GeV. Both the CMS and ATLAS detectors have also shown intensity peaks in the 124–125 GeV range, consistent with either background noise or the observation of the Higgs boson.[87] CHAPTER 1. OVERVIEW 1.2.6 Proposed upgrade Main article: High Luminosity Large Hadron Collider After some years of running, any particle physics experiment typically begins to suffer from diminishing returns: as the key results reachable by the device begin to be completed, later years of operation discover proportionately less than earlier years. A common outcome is to upgrade the devices involved, typically in energy, in luminosity, or in terms of improved detectors. As well as the planned 2013–2015 increase to its intended 14 TeV collision energy, a luminosity upgrade of the LHC, called the High Luminosity LHC, has also been proposed,[94] to be made in 2022. On 22 December 2011, it was reported that a new particle The optimal path for the LHC luminosity upgrade includes an increase in the beam current (i.e. the number had been observed, the χ (3P) bottomonium state.[69] of protons in the beams) and the modification of the two On 4 July 2012, both the CMS and ATLAS teams anhigh-luminosity interaction regions, ATLAS and CMS. nounced the discovery of a boson in the mass region To achieve these increases, the energy of the beams at around 125–126 GeV, with a statistical significance at the point that they are injected into the (Super) LHC the level of 5 sigma. This meets the formal level required should also be increased to 1 TeV. This will require an upto announce a new particle which is consistent with the grade of the full pre-injector system, the needed changes Higgs boson, but scientists were cautious as to whether it in the Super Proton Synchrotron being the most expenis formally identified as actually being the Higgs boson, sive. Currently the collaborative research effort of LHC pending further analysis.[88] Accelerator Research Program, LARP, is conducting reOn 8 November 2012, the LHCb team reported on an search into how to achieve these goals.[95] experiment seen as a “golden” test of supersymmetry theories in physics,[72] by measuring the very rare decay of the B meson into two muons (B 0 → μ+ μ− ). 1.2.7 Cost The results, which match those predicted by the nonsupersymmetrical Standard Model rather than the pre- See also: List of megaprojects dictions of many branches of supersymmetry, show the decays are less common than some forms of supersymWith a budget of 7.5 billion euros (approx. $9bn or metry predict, though could still match the predictions of £6.19bn as of June 2010), the LHC is one of the most exother versions of supersymmetry theory. The results as pensive scientific instruments[96] ever built.[97] The total initially drafted are stated to be short of proof but at a cost of the project is expected to be of the order of 4.6bn relatively high 3.5 sigma level of significance.[89] The reSwiss francs (SFr) (approx. $4.4bn, €3.1bn, or £2.8bn sult was later confirmed by the CMS collaboration.[90] as of Jan 2010) for the accelerator and 1.16bn (SFr) (apIn August 2013 the team revealed an anomaly in the an- prox. $1.1bn, €0.8bn, or £0.7bn as of Jan 2010) for the gular distribution of B meson decay products which could CERN contribution to the experiments.[98] not be predicted by the Standard Model; this anomaly The construction of LHC was approved in 1995 with a had a statistical certainty of 4.5 sigma, just short of the 5 budget of SFr 2.6bn, with another SFr 210M towards the sigma needed to be officially recognized as a discovery. experiments. However, cost overruns, estimated in a maIt is unknown what the cause of this anomaly would be, jor review in 2001 at around SFr 480M for the accelalthough the Z' boson has been suggested as a possible erator, and SFr 50M for the experiments, along with a candidate.[91] reduction in CERN’s budget, pushed the completion date On 19 November 2014, the LHCb experiment announced from 2005 to April 2007.[99] The superconducting magthe discovery of two new heavy subatomic particles, Ξ′− nets were responsible for SFr 180M of the cost increase. b and Ξ∗− There were also further costs and delays due to engib. Both of them are baryons that are composed of one neering difficulties encountered while building the underbottom, one down, and one strange quark. They are ex- ground cavern for the Compact Muon Solenoid,[100] and cited states of the bottom Xi baryon.[92][93] also due to faulty parts provided by Fermilab.[101] Due to lower electricity costs during the summer, the LHC normally does not operate over the winter months,[102] although an exception over the 2009/10 winter was made to make up for the 2008 start-up delays. 15×1011 protons per world.[110] including ultra-highto break 10-ton magnets from their mountings. Details are available experiments in a statement from Fermilab. with which CERN is in agreement. The distributed computing project LHC@home was 1.[107] In Auassemblies.[103] Loss of only one ten-millionth part (10−7 ) of the beam [104] The LHC Computing Grid was constructed to han.the beam dump must absorb 362 MJ (87 kilograms of porated both private fiber optic cable links and existing TNT) for each of the two beams.[117][118] Repairing the broken magnet The experiments at the Large Hadron Collider sparked and reinforcing the eight identical assemblies used fears that the particle collisions might produce doomsby LHC delayed the startup date.2.[115] ning Mac OS X. would fill the volume of one grain of fine sand. This sults.0×10−9 gram of hydroThe Open Science Grid is used as the primary infrastruc. with soot. was estimated at approximately 15 petabytes per (173 kilograms of TNT).9 Safety of particle collisions sign. in standard conditions for temperature and ture in the United States. a conclusion expressly endorsed by It is currently believed that a faulty electrical conthe American Physical Society. when an commissioned safety reviews examined these conelectrical fault in the bus between magnets caused cerns and concluded that the experiments at the LHC a rupture and a leak of six tonnes of liquid helium. enabling cian.2.2. Windows or Linux. and the start of operations was further postponed to midNovember 2009. the beam pipes contain 1. was not strong enough to withstand the forces genMain article: Safety of high energy particle collision erated during pressure testing.8 17 Computing resources beams. as well as LHC-related simu.[112] nection between two magnets caused an arc.[105] bunch). a second application went live (Test4Theory) one was injured.gen. Fermilab director Pier Oddone which performs simulations against which to compare acstated “In this case we are dumbfounded that we tual test data. fault had been present in the original design.2. LARGE HADRON COLLIDER 1.[116] Analysis revealed that its de1.2. No gust 2011.10 Operational challenges cio Rossi.[50][120] This accident was thoroughly discussed in a 22 February 2010 Superconductor Science and Technology article by CERN physicist Lu1. The project uses the BOINC platform. was killed in the LHC when a switchgear that anybody with an Internet connection and a computer runwas being transported fell on him. the total energy stored in the magnets is 10 GJ (2. It incor.[121] The size of the LHC constitutes an exceptional engineering challenge with unique operational issues on account of the amount of energy stored in the magnets and the • Two vacuum leaks were identified in July 2009. Once collision events which exist in the LHC and similar experthe cooling layer was broken.[106] to use their computer’s idle time to simulate how particles will travel in the • On 27 March 2007 a cryogenic magnet support tunnel. 1. the scientists will be able broke during a pressure test involving one of the to determine how the magnets should be calibrated to gain LHC’s inner triplet (focusing quadrupole) magnet the most stable “orbit” of the beams in the ring.pressure. the helium flooded iments occur naturally and routinely in the universe withthe surrounding vacuum layer with sufficient force out hazardous consequences. energy cosmic rays observed to impact Earth with enerThe explosion also contaminated the proton tubes gies far higher than those in any man-made collider.[55] . present no danger and that there is no reason for The operation was delayed for several months. These energies are carhigh-speed portions of the public Internet. microscopic black holes or the creation of hypo• Problems occurred on 19 September 2008 during thetical particles called strangelets. involving the production of stable November 2007.[41][113] While operating.is sufficient to quench a superconducting magnet. enabling data ried by very little matter: under nominal operating contransfer from CERN to academic institutions around the ditions (2.1. a techniLHC. then planned for day phenomena. which The reports also noted that the physical conditions and compromised the liquid-helium containment. and remained during four engineering reviews over the following years.11 Construction accidents and delays started to support the construction and calibration of the • On 25 October 2005.total energy carried by the two beams reaches 724 MJ lation.[119] [109][110][111] concern.400 kilograms of TNT) and the Data produced by LHC. which. and also as part of an interop. José Pereira Lages. provided by Fermilab and KEK. while dle the massive amounts of data produced. made as thin as possible for better insulation. to determine confidence levels of the remissed some very simple balance of forces”. With this information.[108] Two CERNpowering tests of the main dipole circuit.808 bunches per beam. erable federation with the LHC Computing Grid.[114] year (max throughput while running not stated). The Daily Telegraph (London). named SERN.13 See also • Compact Linear Collider The Large Hadron Collider gained a considerable amount of attention from outside the scientific community and its progress is followed by most popular science media. [5] “What is LHCb”. [12] “First beam in the LHC – Accelerating science” (Press release).edu. CERN published a “Science and Fiction” page interviewing Sawyer and physicists about the book and the TV series based on it.[131] “What is the Worldwide LHC Computing Grid?". 10 September 2008.[124] CERN employee Katherine McAlpine's “Large Hadron Rap”[125] surpassed 7 million YouTube views. OVERVIEW Popular culture 1. “Collider halted until next year”. fort to make the science in the story more accurate. “Large Hadron Collider: Thirteen ways to change the world”. Episode 6 “Atom Smasher” features the replacement of the last superconducting magnet section in the repair of the supercollider after the 2008 quench [8] incident. met with CERN experts in an ef. distribute and analyse the ~25 Petabytes (25 million Gigabytes) of data annually generated by the Large Hadron Collider” The third season of the popular CBS sitcom “The Big [11] What is the Worldwide LHC Computing Grid? (PubBang Theory” features an episode revolving around a lic 'About' page) 14 November 2012: “Currently WLCG is made up of more than 170 computing centers in 36 dilemma regarding a trip to Switzerland to see the Large countries.[126][127] The band Les Horribles Cernettes was founded by women from CERN. [4] Highfield. and eventual world domination. January 2011.cern. engineering. CERN. by Robert J.[9] planations of the function.[128][129] [3] “Towards a superforce”. [7] Season 2 (2010).2. Retrieved 2010-04-02.. by Dan Brown. 2008. Retrieved 2012-07-05. the director. It won the Sheffield International Doc/Fest in 2013. involves the search for the Higgs boson at the LHC. and ex. CERN Press Office. vide a conceptual framework for the LHC’s results.[123] The novel FlashForward. Roger (16 September 2008).purdue. CERN Press Office. Hunt for Higgs boson hits key decision point Worldwide LHC Computing Grid main page 14 November 2012: "[A] global collaboration of more than 170 computing centres in 36 countries . to store. “Large Hadron Collider rewards scientists watching at Caltech”. with the movie being filmed on location in CERN’s maintenance tunnels. Ron Howard.web. National Geographic Channel's World’s Toughest Fixes.[132] 20 November 2009. ing grid” The feature documentary Particle Fever follows the experimental physicists at CERN who run the experiments. • International Linear Collider • Very Large Hadron Collider • List of accelerators in particle physics • High Luminosity Large Hadron Collider The novel Angels & Demons.The WLCG is now the world’s largest computHadron Collider. Los Angeles Times. The name was chosen so to have the same initials as the LHC.Gate developed by [15] Large Hadron Collider. In response CERN published a “Fact or Fiction?" page discussing the accuracy of the book’s portrayal of the LHC. Retrieved 2010-04-02.. video games and films. involves • Particle Fever antimatter created at the LHC to be used in a weapon against the Vatican. January 2011. ing Random Things Into Large Hadron Collider”. Retrieved 200810-10. Retrieved 2008-10-09. Physics. and purpose of [10] the LHC.12 CHAPTER 1. 44.ch/topics/large-hadron-collider filmed on-site at one of the experiments at the LHC. [13] Paul Rincon (23 September 2008).. CERN.[2] “Missing Higgs”. CERN Communication Group. CERN. 2008. the Large Hadron Collider is utilized by the game′s parody of CERN. Reas well as the theoretical physicists who attempt to protrieved 2008-10-09. In the Japanese visual novel Steins.2. CERN FAQ. Retrieved 2008-10-10. January 2008. The episode includes actual footage from the repair facility to the inside of the supercollider. and Nitroplus. Onion News Network featured a parodied news story about the LHC titled “Bored Scientists Now Just Stick[14] “Large Hadron Collider – Purdue Particle Physics”.2. [6] Amina Khan (31 March 2010). 5pb.[122] The movie version of the book has footage [1] http://home.18 1. “Welcome”.[130] The Large Hadron Collider was the focus of the 2012 student film Decay. Retrieved 2012-01-11. Retrieved 2012-0111. BBC News. The LHC has also inspired works of fiction including novels. Retrieved 2008-10-10.. CERN. .14 References general. for time [16] “The LHC is back” (Press release). p. CERN. TV series. Sawyer. and particle physics in 1. Retrieved 2009-11-20. travel. arXiv:0802. Retrieved 2009-04-17.. [23] G. Pramana 72 (1): 143–160. Hogenboom (24 July 2013). Econf C:l. New Scientist... Scientific American. EDMS 973073. [47] “Interim Summary Report on the Analysis of the 19 September 2008 Incident at the LHC” (PDF). Oxford University Press."This mass threshold means. [25] ". CERN. 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January 2008. long-sought Higgs boson”. summer start-up planned for collider”. Reuters. Steins. The world’s largest particle accelerator. World’s Toughest Fixes. Coordinates: 46°14′N 06°03′E / 46. Retrieved 2009-09-28. “Large Hadron Collider Unleashes Rampaging Zombies”. doi:10.3S8001E. Rebecca (2012-10-31). from Boston Globe. Popular Mechanics. Retrieved 4 March 2014. [125] Katherine McAlpine (28 July 2008). Brady Haran for the University of Nottingham. [129] Heather McCabe (10 February 1999). “Physicists Discover Another Unifying Force: Doo-Wop”. • Podcast Interview with CERN’s Rolf Landua about the LHC and the physics behind it • “Petabytes at the LHC”. [130] “Atom Smashers”.22 CHAPTER 1.Gate..15 External links • Official website • Overview of the LHC at CERN’s public webpage • CERN Courier magazine • LHC Portal Web portal • CERN. Wired News. Retrieved 15 June 2014. [126] Roger Highfield (6 September 2008). Retrieved 2010-09-21. Bibcode:2008JInst. September 2009. • NYTimes: A Giant Takes On Physics’ Biggest Questions.19 September 2008 incident repair. “Grrl Geeks Rock Out”. Journal of Instrumentation 3 (8): S08001. “Large Hadron Rap”. OVERVIEW [124] “FlashForward”. how it works on YouTube • Lyndon Evans and Philip Bryant (eds) (2008). • Why a Large Hadron Collider? Seed Magazine interviews with physicists.wiki. “Large Hadron Collider rap teaches particle physics in 4 minutes”. Episode 6. [128] Malcolm W Brown (29 December 1998). http://natgeotv. Season 2. Daily Telegraph (London).aspx?id=100.2. 1.com. • Thirty collected pictures during commissioning and post. Sixty Symbols. Retrieved 2009-10-03. [132] “SERN”. “Rap about world’s largest science experiment becomes YouTube hit”. National Geographic Channel. Retrieved 2010-09-21. Retrieved 2009-09-28.233°N 6.1088/1748-0221/3/08/S08001. CERN. Retrieved 2011-05-08. Full documentation for design and construction of the LHC and its six detectors (1600p). “LHC Machine”. [127] Jennifer Bogo (1 August 2008). YouTube.050°E . Retrieved 22 November 2012. [131] Boyle. • New Yorker: Crash Course. New York Times.au/tv/world%27s-toughest-fixes/ episode.. “MoEDAL becomes the LHC’s magnificent seventh”. The LHC is the most energetic [1] Previously Fabiola Gianotti particle collider in the world. “SPIRES database”. Large Hadron Collider experiments See also: Large Hadron Collider CERN. “CERN Research Board Approves the MoEDAL Experiment”. The list is first compiled from the SPIRES database.1 [2] James Pinfold (2010). e.1. 2. 23 .1. 5 May 2010 • SPIRES team. and will be used to test the accuracy of the Standard Model (and particularly to search for the Higgs boson).1. at the CERN Large Hadron Collider (LHC).020139°E ALICE (A Large Ion Collider Experiment) is one of seven detector experiments at the Large Hadron Collider at CERN. • GS-AIF-FPF.1. “Grey Book”. extra dimen[1] James Pinfold (2010). then missing information is retrieved from the online version CERN’s Grey Book.1 List of Large Hadron Collider experiments • LEP: Large Electron–Positron Collider • LHC: Large Hadron Collider This is a list of current and proposed experiments that 2.2 A Large Ion Collider Experiment Coordinates: 46°15′04. Retrieved 2009-09-15.Chapter 2 Experiments 2. The MoEDAL Milestone Blog. The other six are: ATLAS. LHCb. and look for physics beyond 2. CMS. 2010-04-11. or would take place. 2009-09-15. When there is a conflict between the SPIRES database and the Grey Book.2 • LHC website See also • CERN Grey Book Experiments • SPIRES database • List of Super Proton Synchrotron experiments Facilities • CERN: European Organization for Nuclear Research • PS: Proton Synchrotron • SPS: Super Proton Synchrotron • ISOLDE: On-Line Isotope Mass Separator • ISR: Intersecting Storage Rings 2. “The MoEDAL TDR”. Retrieved 2010-04-11.8″N 6°01′12. if the SPIRES database lists December 2008. the Grey Book entry is shown.251333°N 6. the SPIRES database information is listed. LHCf and MoEDAL.3 Notes take place.5″E / 46. Retrieved 2. unless otherwise noted. Retrieved sions.g. while the Grey Book lists 22 December 2008. The most specific information of the two is kept.4 References the Standard Model such as supersymmetry. TOTEM. [3] CERN Courier. and others.1. Stanford Linear Accelerator Center.5 External links • CERN website 2. From the ideas presented there. even if their relevance may only become apparent later and flexible. including the electrical and cooling is believed to have taken place when the universe was systems. allowing additions and modifications along the way as new avenues of investigation would open up. ALICE is optimized to study heavy-ion (Pb-Pb nuclei) collisions at a centre of mass energy of 2. The existence of 1995. a LoI was submitted. Recreatat the LHC in 2010.[4] 2.[1] 2. Significant advances. and gluons and the nature of strong interactions and how they result in generating the bulk of the mass of ordinary After more than three years of successful operation. which was sustained over most of the 1990s. well organised and well supported R&D effort. Various major detecALICE is focusing on the physics of strongly interact.76 TeV per nucleon pair. Similar conditions are believed to existed a fraction of the second after the Big Bang before quarks and gluons bound together to form hadrons and heavier particles.3 Heavy-Ion Collisions at the LHC Searches for Quark Gluon plasma and a deeper understanding of the QCD started at CERN and Brookhaven with lighter ions in the 1980s.[2][3] the world. and later complemented by an additional forward muon spectrometer designed in 1995. as it included a number of observables in its initial menu whose importance only became clear later. of consolidation and upgrade during the long shutdown of Quantum chromodynamics (QCD) predicts that at suffiCERN’s accelerator complex.2. A new subdetector called ciently high energy densities there will be a phase tranthe dijet calorimeter (DCAL) will be installed.24 2. it became clear from the outset that also the challenges of heavy ion physics at LHC could not be really met (nor paid for) with existing technology. and all sition from conventional hadronic matter. from the muon spectrometer in ing matter at extreme energy densities. Like for all other LHC experiments. The initially very broad and later more focused. and in some cases a technological break-through. would be required to built on the ground what physicists had dreamed up on paper for their experiments.1 CHAPTER 2.2. Data sets taken during heavy-ion ing this primordial form of matter and understanding how periods in 2010 and 2011 as well as proton-lead data from it evolves is expected to shed light on questions about how 2013 have provided an excellent basis for an in-depth look matter is organized.2 History The idea of building a dedicated heavy-ion detector for the LHC was first aired at the historic Evian meeting “Towards the LHC experimental Programme” in March 1992. and may still play a role today in the the very intense upgrade programme of ALICE have athearts of collapsing neutron stars or other astrophysical tracted numerous institutes and scientists from all over objects. the mechanism that confines quarks at the physics of quark–gluon plasma. EXPERIMENTS Introduction Computer generated cut-away view of ALICE showing the 18 detectors of the experiment. ALICE received the green light from the LHC Committee to proceed towards final design and construction. The resulting temperature and energy density are expected to be high enough to produce quark– gluon plasma. electronics and computing. The detector had to be general purpose . in Quantum Chromodynamics for understanding Color ALICE recorded data from the first lead-lead collisions confinement and Chiral symmetry restoration. Today the ALICE Collaboration has more than 1300 members coming from 110 institutes in 36 countries. are locked inside nuclear particles.able to measure most signals of potential interest. the transition radiation detectors in 1999 to a large the quark–gluon plasma and its properties are key issues jet calorimeter added in 2007. The reverse of this transition ICE infrastructure. the ALICE detector is about to undergo a major programme matter. where quarks 18 of the existing ALICE subdetectors will be upgraded.2. has led to many evolutionary and some revolutionary advances in detectors. In 1997. In both respects ALICE did quite well. Designing a dedicated heavy-ion experiment in the early '90s for use at the LHC some 15 years later posed some daunting challenges.[6][7] Today’s programme at ALICE was first proposed as a central detector in 1993 these laboratories has moved on to ultrarelativistic col- . The wealth of published scientific results and just 10−6 sec old. the ALICE collaboration was formed and in 1993. to a plasma of deconThere will also be major renovation work on the ALfined quarks and gluons.tion system where added. a state of matter wherein quarks and gluons are freed.[5] The first ten years were spent on design and an extensive R&D effort. and the LHC ac- 2. One of the LHC’s first lead-ion collisions. or a total collision energy of 574 TeV. This involves making the most . Proton-lead collisions are an ideal tool for this study.000 times higher than the temperature in the core of the sun. made of three quarks. The colors of the lines indicate how much energy each particle carried away from the collision.heating up matter in the interaction point to a temperature almost 100. The quark–gluon plasma is formed as proton and neutrons “melt” into their elementary constituentsm. In order to study if part of the effects we see when comparing leadlead and proton-proton collisions is due to this configuration difference rather than the formation of the plasma. and is just reaching the energy threshold at which the phase transition is expected to occur. which may combine to form the nuclei of on 13 September 2012 at a center of mass energy per colliding antiatoms as heavy as helium. the configurations of the quarks and gluons that make up the protons and neutrons of the incoming lead nucleus can be somewhat different of those in the incoming protons. protons and neutrons.2.e. CET. and to determine their charge. Lead ions are accelerated to 99. hundreds of protons and neutrons smash into one another at energies of upwards of a few TeVs. During head-on collisions of lead ions at the LHC. quarks and gluons become asymptotically free. will push the energy reach even further. The Large Hadron Collider smashed its first lead ions in 2010.4 The ALICE detectors A key design consideration of ALICE is the ability to study QCD and quark (de)confinement under these extreme conditions.02 TeV. and even copious antiprotons and Proton-Lead ion collision recorded by the ALICE Experiment antineutrons. ATLAS and CMS collisions took place less than 72 hours after the LHC ended its first run of protons and switched to accelerating lead-ion beams. the so-called quark–gluon plasma which is believed to have filled the universe a few microseconds after the Big Bang.5 TeV. ALICE’s physics programme relies on being able to identify all of them.5 TeV/nucleon.9% of the speed of light and collisions at the LHC are 100 times more energetic than those of protons . In the case of lead-lead collisions. This is done by using particles. that live long enough to reach the sensitive detector layers situated around the interaction region. to determine if they are electrons. A LARGE ION COLLIDER EXPERIMENT lisions of heavy ions.2. The LHC.2.m.[11] The first leadFirst Lead-Lead Collisions proton run at the LHC lasted for one month and data help ALICE physicists to decouple the effects of the plasma from effects that stem from cold nuclear matter effects and shed more light on the study of the Quark-Gluon plasma. i. matter undergoes a transition to form for a brief instant a droplet of primordial matter. Each lead nucleus contains 82 protons. studying the distribution and energy of this debris. Proton-lead collisions at the LHC When the two lead nuclei slam into each other.000 charged particles were emitted from each collision.[9][10] The first collisions in the center of the ALICE. shown here as lines radiating from the collision point. on 7 November at around 12:30 a. created inside the hot volume as it expands and cools down. 25 celerates each proton to an energy of 3. pions. as recorded by the ALICE detector. Up to 3. Much can be learned by nucleon-nucleon pair of 5. which are made of a quark and an antiquark. In 2013. photons. the LHC collided protons with lead ions for the LHC’s first physics beams of 2013. with a centre-of-mass energy around 5. The droplet of QGP instantly cools. thus resulting in an energy of 287 TeV per beam.[8] The debris contains particles such as pions and kaons. and the individual quarks and gluons (collectively called partons) recombine into a blizzard of ordinary matter that speeds away in all directions. etc. However. Overall view of the ALICE detector of the (sometimes slightly) different ways that particles interact with matter. . The experiment is divided into a few main components and each component tests a specific set of particle properties. tracking efficiency at low pT and readout rate capabilities. ITS Drift. the ITS has been made as lightweight and delicate as possible. The ITS is so precise that particles which are generated by the decay of other particles with a very short life time can be identified by seeing that they do not originate from Installation of the ALICE Inner Tracking System Inner Tracking System The short-living heavy particles cover a very small distance before decaying. EXPERIMENTS the point where the interaction has taken place (the “vertex” of the event) but rather from a point at a distance of as small as a tenth of a millimeter. This system aims at identifying these phenomena of disintegration by measuring the location where they occur with a precision of a tenth of millimetre. it is the largest system using both types of silicon detector.[12] In a “traditional” experiment. by the characteristic signatures they leave in the detector. pin-pointing their position of passage to a fraction of a millimetre.[14] The Inner Tracking System (ITS) consists of six cylindrical layers of silicon detectors. ALICE has recently presented plans for an upgraded Inner Tracking System. The ALICE tracking detectors are embedded in a magnetic field of 0. bending the trajectories of the particles: from the curvature of the tracks one can find their momentum.26 CHAPTER 2.[15] With the help of the ITS particles containing heavy quarks (charm and beauty) can be identified by reconstructing the coordinates at which they decay. and is used for example by the large LHC experiments ATLAS and CMS. The layers surround the collision point and measure the properties of the particles emerging from the collisions. • 2 layers of SSD (Silicon Strip Detector). The detectors are embedded in a magnetic field in order to bend the tracks of charged particles for momentum and charge determination. the velocity and the electrical sign of the particles. ITS Strips) the TPC and the TRD measure at many points the passage of each particle carrying an electric charge and give precise information about the particle’s trajectory. The ITS was inserted at the heart of the ALICE experiment in March 2007 following a large phase of R&D. This method for particle identification works well only for certain particles. The Inner Tracking System (consisting of three layers of detectors: ITS Pixels. Tracking Particles An ensemble of cylindrical detectors that surround the interaction point is used to track all the particles that fly out of the hot medium. mainly based on building a new silicon tracker with greatly improved features in terms of determination of the impact parameter (d0) to the primary vertex. ITS layers (counting from the interaction point): • 2 layers of SPD (Silicon Pixel Detector). These components are stacked in layers and the particles go through the layers sequentially from the collision point outwards: first a tracking system. • 2 layers of SDD (Silicon Drift Detector). this technique is not suitable for hadron identification as it doesn't allow distinguishing the different charged hadrons that are produced in Pb-Pb collisions. With almost 5 m2 of double-sided silicon strip detectors and more than 1 m2 of silicon drift detectors.[16] The upgraded ITS will open new channels in the study of the Quark Gluon Plasma formed at LHC which are necessary in order to understand the dynamics of this condensed phase of the QCD.5 Tesla produced by a huge magnetic solenoid. Using the smallest amounts of the lightest material. then an electromagnetic (EM) and a hadronic calorimeter and finally a muon system. In order to identify all the particles that are coming out of the system of the QGP ALICE is using a set of 18 detectors[13] that give information about the mass. particles are identified or at least assigned to families (charged or neutral hadrons). Inside such a radiator.thin materials. Finally. is given by the drift time. which can lead to the emission of TR photons with energies in the X-ray range. jection Chamber (TPC) is a large volume filled with a gas as detection medium and is the main particle track. the upgraded ITS will give us the chance to characterize the thermal radiation coming from the QGP and the in-medium modification of hadronic spectral functions as related to chiral symmetry restoration. because they provide signals with pulse heights proportional to the ionization strength. such as in heavy-ion collisions. electrons can be identified via a combination of Multiwire proportional counters or solid-state counters are often used as detection medium. The characteris. interconnection and packaging technologies. the fact that electrons may create TR when travelling through a dedicated “radiator” can be exploited. In the momentum range 1–10 GeV/c.2. gives the necessary signal amplification. Since energy-loss fluctuations can be considerable.[17][18] positrons can be discriminated from other charged Charged particles crossing the gas of the TPC ionize the particles using the emission of transition radiation. Below atomic electrons of the medium. The ALICE Time Projection Chamber used for particle tracking and identification. 27 pads that form the cathode plane of the multi-wire proportional chambers (MWPC) located at the end plates.[19] In a simidentification. The upgrade project requires an extensive R&D effort by our researchers and collaborators all over the world on cutting-edge technologies: silicon sensors. The readout is performed by the 557 568 PID measurements in the TPC and TOF.The identification of electrons and positrons is achieved ticles passing through a medium can be used for particle using a transition radiation detector (TRD). The straightforward pattern recognition (continuous tracks) make TPCs the perfect choice for highmultiplicity environments. resulting in a resolution of the ionization measurement as good as 5%.2. The positive ions created in the avalanche induce a positive current signal on the pad plane. An avalanche effect in the vicinity of the anode wires strung in the readout chambers. in general many pulse-height measurements are performed along the particle track in order to optimize the resolution of the ionization measurement. The last coordinate. 1 GeV/c. This gives the radial distance to the beam and the azimuth. fast charged particles cross the boundaries between materials with different dielectric constants. but it features a minimum material budget. The completed ALICE detector showing the eighteen TRD mod- Time Projection Chamber The ALICE Time Proules (trapezoidal prisms in a radial arrangement). where thousands of particles have to be tracked simultaneously. which describes the average energy loss of charged resonances.Transition Radiation Detector Electrons and ing device in ALICE. the ionization strength of all tracks is sampled up to 159 times. ultra-light mechanical structures and cooling units. The effect is tiny and the radiator has to provide many hundreds of ma- . Inside the ALICE TPC. tics of the ionization process caused by fast charged par. z along the beam direction. A LARGE ION COLLIDER EXPERIMENT It will allow the study of the process of thermalization of heavy quarks in the medium by measuring heavy flavour charmed and beauty baryons and extending these measurements down to very low pT for the first time. liberating electrons that drift X-rays emitted when the particles cross many layers of towards the end plates of the detector. Almost all of the TPC’s volume is sensitive to the traversing charged particles. this system enstrength is connected to the well-known Bethe-Bloch for. gas atoms along their path. low-power electronics. The velocity dependence of the ionization ilar manner to the muon spectrometer. but with extended coverage down to the light particles through inelastic Coulomb collisions with the vector-meson ρ and in a different rapidity region. It will also give a better understanding of the quark mass dependence of in-medium energy loss and offer a unique capability of measuring the beauty quarks while also improving the beauty decay vertex reconstruction.ables detailed studies of the production of vector-meson mula. a kaon or a pion. 10 gas gaps per MRPC are needed to arrive at a detection efficiency To develop such a Transition Radiation Detector (TRD) close to 100%. EXPERIMENTS the flight time over a given distance along the track trajectory. There are approximately 160 000 MRPC pads with time resolution of about 100 ps distributed over the large surface of 150 square meters. p = 1. In ALICE all of these methods may be combined in order to measure. High Momentum Particle Identification Detector The High Momentum Particle Identification Detector (HMPID) is a RICH detector to determine the speed of particles beyond the momentum range available through energy loss (in ITS and TPC. The radiation propALICE by Time-Of-Flight (TOF). In the ALICE TRD. The MRPCs are parallel-plate detectors built of thin sheets of standard window glass to create narrow gas gaps with high electric fields. or a proton. with an inner radius of 3.7 m. Each of these methods works well in different momentum ranges or for specific types of particle. TOF measurements agates with a characteristic angle with respect to the yield the velocity of a charged particle by measuring particle track.2–1. The ALICE TRD was designed to derive a fast trigger for charged particles with high momentum and can significantly enhance the recorded yields of vector mesons. particle spectra. p = 600 MeV) and through time-of-flight measurements (in TOF. Muons are measured by exploiting the fact that they penetrate matter more easily than most other particles: in the forward region a very thick and complex absorber stops all other particles and muons are measured by a dedicated set of detectors: the muon spectrometer. To obtain the particle velocity there exist four methods based on measurements of time-of-flight and ionization.28 terial boundaries to achieve a high enough probability to produce at least one photon. thus allowing to identify electrons. the TR photons are detected just behind the radiator using MWPCs filled with a xenon-based gas mixture. The ALICE TOF detector is a large-area detector based on multigap resistive plate chambers (MRPCs) that cover a cylindrical surface of 141 m2. Provided the momentum is also known.4 GeV). with a precision better than a tenth of a billionth of a second. The HMPID detector before final installation inside the ALICE magnet. which combines all of the information to search for electron–positron track pairs within only 6 μs. CHAPTER 2. for instance. Combining such a measurement with the PID information from the ALICE also wants to know the identity of each particle. to be built with an overall TOF resolution of 80 ps at a relatively low cost (CERN Courier November 2011 p8). where they deposit their energy on top of the ionization signals from the particle’s track. 250. . and on detection of transition radiation and Cherenkov radiation. The HMPID measures the faint light patterns generated by fast particles and the TRD measures the special radiation very fast particles emit when crossing different materials.000 CPUs are installed right on the detector to identify candidates for high-momentum tracks and analyse the energy deposition associated with them as quickly as possible (while the signals are still being created in the detector). For this purpose. pions Particle Identification with ALICE and protons up to momenta of a few GeV/c. more specialized detectors are needed: the TOF measures. These plates are separated using fishing lines to provide the desired spacing. Momentum and the sign of the charge are obtained by measuring the curvature of the particle’s track in a magnetic field. Cherenkov radiation is a shock wave resulting from charged particles moving through a material faster than Time of Flight Charged particles are identified in the velocity of light in that material. the mass of the particle can then be derived from these measurements. unambiguously identified if their mass and charge are determined. the time that each particle takes to travel from the vertex to reach it. as figure 3 shows Charged hadrons (in fact. all stable charged particles) are for a particular momentum range.[20][21] Using the tracking information from other detectors every track firing a sensor is identified. This information is sent to a global tracking unit. so that one can measure its speed. for ALICE many detector prototypes were tested in The simplicity of the construction allows a large system mixed beams of pions and electrons. In addition to the information given by ITS and TPC. ALICE TPC has proved useful in improving the separawhether it is an electron. tion between the different particle types. which depends on the particle velocity. This performance allows the separation of kaons. The mass can be deduced from measurements of the momentum and of the velocity. All particles except muons and neutrinos deposit all their energy in the calorimeter system by production of electromagnetic or hadronic showers.2. which are as dense as lead and as transparent as glass. . The crystals are kept at a temperature of 248 K. A prototype was successfully tested at CERN in 1997 and RRC “Kurchatov Institute”. but a photon can be identified by the non-existence of a track in the tracking system that is associated to the shower. Such a proximity-focusing RICH is installed in the ALICE experiment.imum deflection between being empty and being fully ties of the initial phase of the collision. The super-modules are inserted into an independent support frame situated within the ALICE magnet.sophisticated insertion device to bridge across to the suppidity. It is the world’s largest A technology for mass production of PWO crystals has been decaesium iodide RICH detector. The complete EMCal will contain from a hot object. the Apatity plant m². and determine whether they have electromagnetic or hadronic interactions. Particle Identification in a calorimeter is a destructive measurement.a smaller. A LARGE ION COLLIDER EXPERIMENT 29 Cherenkov detectors make use of this effect and in general consist of two main elements: a radiator in which Cherenkov radiation is produced and a photon detector. If a dense medium (large refractive index) is used. highly granular leadparticles (called “jets”) which have a memory of the early tungstate calorimeter. Installation of the measuring photons emerging directly from the collision. while the PMD and Time Projection Chamber and central detector. and a in particular the EMCal will measure them over a very third of its azimuth placed back-to-back with the ALICE wide area.[23] similar to port structure.The EMCal covers almost the full length of the ALICE tastic precision in a limited region. the ones used by CMS.optical fiber. tell us about the temperature of the 100. and currently takes data at the Relativistic Heavy Ion Collider at the Brookhaven National Laboratory in the US. When high energy photons strike lead tungstate. Ring imaging Cherenkov (RICH) detectors resolve the ring-shaped image of the focused Cherenkov radiation. with a maxprovide data to test the thermal and dynamical proper.000 individual scintillator tiles and 185 kilometers of system. read out using Avalanche Photodiodes (APD).000 individual towers that are grouped into ten supermodules. To measure them. This is done by loaded of only a couple of centimeters. with an active area of 11 veloped in close cooperation between CERN. Electro-Magnetic Calorimeter The EMCal is a lead-scintillator sampling calorimeter comprising almost 13. Lead tungstate is extremely dense (denser than iron). sary: the crystals of the PHOS. weighing in total about 100 tons. special detectors are neces. allowing the cone of light to expand and form the characteristic ring-shaped image. The EMCal will also measure groups of close Photon Spectrometer . and this glow can be measured. enabling a measurement of the Cherenkov angle and thus the particle velocity. The supPhoton Spectrometer PHOS is a high-resolution port frame itself is a complex structure: it weighs 20 tons electromagnetic calorimeter installed in ALICE[22] to and must support five times its own weight. phases of the event. This in turn is sufficient to determine the mass of the charged particle. The towers are read out by wavelength-shifting optical fibers in a shashlik geometry coupled to an The photons (particles of light). Their showers are indistinguishable.2. like the light emitted avalanche photodiode. Calorimeters Calorimeters measure the energy of particles. will measure them with fan. between the time-of-flight counters and the magnet coil. stopping most photons that reach it. It is made of lead tungstate crystals. Photons. or scintillate. which helps to minimize the deterioration of the energy resolution due to noise and to optimize the response for low energies. only a thin radiator layer of the order of a few centimetres is required to emit a sufficient number of Cherenkov photons. eight-ton super-modules requires a system of rails with a PHOS covers a limited acceptance domain at central ra. electrons and positrons deposit all their energy in an electromagnetic calorimeter. ALICE HMPID’s momentum range is up to 3 GeV for pion/kaon discrimination and up to 5 GeV for kaon/proton discrimination. they make it glow. The photon detector is then located at some distance (usually about 10 cm) behind the radiator. 30 The Electro-Magnetic Calorimeter (EM-Cal) will add greatly to the high momentum particle measurement capabilities of ALICE.[24] It will extend ALICE’s reach to study jets and other hard processes. CHAPTER 2. EXPERIMENTS charmonium states (J/Ψ and Ψ′) as well as the bottomonium states (ϒ, ϒ′ and ϒ′′) can be studied. The Dimuon spectrometer is optimized for the detection of these heavy quark resonances. Photon Multiplicity Detector The Photon Multiplicity Detector (PMD) is a Particle shower detector which measures the multiplicity and spatial distribution of photons produced in the collisions.[25] It utilizes as a first layer a veto detector to reject charged particles. Photons on the other hand pass through a converter, initiating an electromagnetic shower in a second detector layer where they produce large signals on several cells of its sensitive volume. Hadrons on the other hand normally affect only one The main components of the ALICE muon spectrometer: an abcell and produce a signal representing minimum-ionizing sorber to filter the background, a set of tracking chambers before, inside and after the magnet and a set of trigger chambers. particles. Muons may be identified using the just described technique by using the fact that they are the only charged particles able to pass almost undisturbed through any material. This behaviour is connected to the fact that muons with momenta below a few hundred GeV/c do not suffer from radiative energy losses and so do not produce electromagnetic showers. Also, because they are leptons, they are not subject to strong interactions with the nuclei of the material they traverse. This behaviour is exploited in muon spectrometers in high-energy physics experiments by installing muon detectors behind the calorimeter systems or behind thick absorber materials. All charged parALICE Forward Multiplicity Detector ticles other than muons are completely stopped, producForward Multiplicity Detectors The Forward Mul- ing electromagnetic (and hadronic) showers. tiplicity Detector (FMD) extends the coverage for multi- The muon spectrometer in the forward region of ALICE plicity of charge particles into the forward regions - giving features a very thick and complex front absorber and an ALICE the widest coverage of the 4 LHC experiments for additional muon filter consisting of an iron wall 1.2 m these measurements.[26] thick. Muon candidates selected from tracks penetrating these absorbers are measured precisely in a dedicated set of tracking detectors. Pairs of muons are used to collect the spectrum of heavy-quark vector-meson resonances (J/Psi). Their production rates can be analysed as a function of transverse momentum and collision centrality in order to investigate dissociation due to colour screening. The acceptance of the ALICE Muon Spectrometer covers the pseudorapidity interval 2.5 ≤ η ≤ 4 The forward detectors also comprise the main trigger deand the resonances can be detected down to zero transtectors for timing (T0) and for collision centrality (V0). verse momentum. FMD consist of 5 large silicon discs with each 10 240 individual detector channels to measure the charged particles emitted at small angles relative to the beam. FMD provides an independent measurement of the orientation of the collisions in the vertical plane, which can be used with measurements from the barrel detector to investigate flow, jets, etc. Muon Spectrometer The ALICE forward muon spectrometer studies the complete spectrum of heavy quarkonia (J/Ψ, Ψ′, ϒ, ϒ′, ϒ′′) via their decay in the μ+μ– channel. Heavy quarkonium states, provide an essential tool to study the early and hot stage of heavy-ion collisions.[27] In particular they are expected to be sensitive to QuarkGluon Plasma formation. In the presence of a deconfined medium (i.e. QGP) with high enough energy density, quarkonium states are dissociated because of colour screening. This leads to a suppression of their production rates. At the high LHC collision energy, both the Characterization of the Collision Finally, we need to know how powerful the collision was: this is done by measuring the remnants of the colliding nuclei in detectors made of high density materials located about 110 meters on both sides of ALICE (the ZDC’s) and by measuring with the FMD, V0 and T0 the number of particles produced in the collision and their spatial distribution. T0 also measures with high precision the time when the event takes place. 2.2. A LARGE ION COLLIDER EXPERIMENT 31 Front face of the ZN calorimeter: One of the two ZN calorimeters during assembly. The quartz fibers are hosted in the 1936 grooves of the W-alloy slabs. Zero Degree Calorimeter The ZDCs are calorimeters which detect the energy of the spectator nucleons in order to determine the overlap region of the two colliding nuclei. It is composed of four calorimeters, two to detect protons (ZP) and two to detect neutrons (ZN). They are located 115 meters away from the interaction point on both sides, exactly along the beam line. The ZN is placed at zero degree with respect to the LHC beam axis, between the two beam pipes. That is why we call them Zero Degree Calorimeters (ZDC).The ZP is positioned externally to the outgoing beam pipe. The spectator protons are separated from the ion beams by means of the dipole magnet D1. An array of Cherenkov counters used in the ALICE T0 detector. T0 supplies five different trigger signals to the Central Trigger Processor. The most important of these is the T0 vertex providing prompt and accurate confirmation of the location of the primary interaction point along the beam axis within the set boundaries. The detector is also used for online luminosity monitoring providing fast feedback to the accelerator team. The T0 detector consists of two arrays of Cherenkov counters (T0-C and T0-A) positioned at the opposite sides of the interaction point (IP). Each array has 12 cylindrical counters equipped with a quartz radiator and The ZDCs are “spaghetti calorimeters”, made by a stack a photomultiplier tube. of heavy metal plates grooved to allocate a matrix of quartz fibres. Their principle of operation is based on ALICE Cosmic Rays Detector (ACORDE) the detection of Cherenkov light produced by the charged particles of the shower in the fibers. The ALICE underground cavern provides an ideal place for the detection of high energy atmospheric muons comV0 Detector V0 is made of two arrays of scintillator ing from cosmic ray showers. ACORDE detects cosmic counters set on both sides of the ALICE interaction point, ray showers by triggering the arrival of muons to the top and called V0L and V0R respectively. The V0R counter of the ALICE magnet. will be located right upstream of the dimuon arm ab- The ALICE cosmic ray trigger is made of 60 scintillator sorber and cover the spectrometer acceptance while the modules distributed on the 3 upper faces of the ALICE V0L counter will be located at around 3.5 m away from magnet yoke. The array can be configured to trigger on the collision vertex, on the other side. single or multi-muon events, from 2-fold coincidences up It is used to estimate the centrality of the collision by summing up the energy deposited in the two disks of Vzero. This observable scales directly with the number of primary particles generated in the collision and therefore to the centrality. to the whole array if desired. ACORDE’s high luminosity allows the recording of cosmic events with very high multiplicity of parallel muon tracks, the so-called muon bundles. With ACORDE, the ALICE Experiment has been able V0 is also used as reference in Van Der Meer scans that to detect muon bundles with the highest multiplicity ever give the size and shape of colliding beams and therefore registered as well as to measure very high energy primary cosmic rays. the luminosity delivered to the experiment. T0 Detector ALICE T0 serves as a start, trigger and 2.2.5 Data Acquisition luminosity detector for ALICE. The accurate interaction time (START) serves as the reference signal for the Time- ALICE had to design a data acquisition system that operof-Flight detector that is used for particle identification. ates efficiently in two widely different running modes: the 32 CHAPTER 2. EXPERIMENTS very frequent but small events, with few produced particles encountered during proton-proton collisions and the relatively rare, but extremely large events, with tens of thousands of new particles produced in lead-lead collisions at the LHC (L = 1027 cm−2 s−1 in Pb-Pb with 100 ns bunch crossings and L = 1030 −1031 cm−2 s−1 in pp with 25 ns bunch crossings).[28] The ALICE data acquisition system needs to balance its capacity to record the steady stream of very large events resulting from central collisions, with an ability to select and record rare cross-section processes. These requirements result in an aggregate event building bandwidth of up to 2.5 GByte/s and a storage capability of up to 1.25 GByte/s, giving a total of more than 1 PByte of data every year. As shown in the figure, ALICE needs a data storage capacity that by far exceeds that of the current Events recorded by the ALICE experiment from the first lead ion collisions, at a centre-of-mass energy of 2.76 TeV per nucleon generation of experiments. This data rate is equivalent pair. to six times the contents of the Encyclopædia Britannica every second. The hardware of the ALICE DAQ system[29] is largely based on commodity components: PC’s running Linux and standard Ethernet switches for the eventbuilding network. The required performances are achieved by the interconnection of hundreds of these PC’s into a large DAQ fabric. The software framework of the ALICE DAQ is called DATE (ALICE Data Acquisition and Test Environment). DATE is already in use today, during the construction and testing phase of the experiment, while evolving gradually towards the final production system. Moreover, AFFAIR (A Flexible Fabric and Application Information Recorder) is the performance monitoring software developed by the ALICE Data Acquisition project. AFFAIR is largely based on open source code and is composed of the following components: data gathering, inter-node communication employing DIM, fast and temporary round robin database storage, and permanent storage and plot generation using ROOT. that occur in the medium and the dependencies of energy loss on the parton species, iii) the dissociation of quarkonium states which can be a probe of deconfinement and of the temperature of the medium and finally the production of thermal photons and low-mass dileptons emitted by the QGP which is about assessing the initial temperature and degrees of freedom of the systems as well as the chiral nature of the phase transition. The ALICE collaboration presented its first results from LHC proton collisions at a centre-of-mass energy of 7 TeV in March 2010.[30] The results confirmed that the charged-particle multiplicity is rising with energy faster than expected while the shape of the multiplicity distribution is not reproduced well by standard simulations. The results were based on the analysis of a sample of 300,000 proton–proton collisions the ALICE experiment collected during the first runs of the LHC with stable Finally. the ALICE experiment Mass Storage System beams at a centre-of-mass energy, √s, of 7 TeV, (MSS) combines a very high bandwidth (1.25 GByte/s) In 2011, the ALICE Collaboration measured the size of and every year stores huge amounts of data, more than 1 the system created in Pb-Pb collisions at a centre-of-mass Pbytes. The mass storage system is made of: a) Global energy of 2.76 TeV per nucleon pair.[31] ALICE conData Storage (GDS) performing the temporary storage of firmed that the QCD matter created in Pb-Pb collisions data at the experimental pit; b) Permanent Data Storage behaves like a fluid, with strong collective motions that (PDS) for long-term archive of data in the CERN Com- are well described by hydrodynamic equations. The fireputing Center and finally from The Mass Storage Sys- ball formed in nuclear collisions at the LHC is hotter, lives tem software managing the creation, the access and the longer and expands to a larger size than the medium that archive of data. was formed in heavy-ion collisions at RHIC. Multiplic- 2.2.6 Results The physics programme of ALICE includes the following main topics: i) the study of the thermalization of partons in the QGP with focus on the massive charm and beauty quarks and understanding the behaviour of these heavy quarks in relation to the stroungly-coupled medium of QGP, ii) the study of the mechanisms of energy loss ity measurements by the ALICE experiment show that the system initially has much higher energy density and is at least 30% hotter than at RHIC, resulting in about double the particle multiplicity for each colliding nucleon pair (Aamodt et al. 2010a). Further analyses, in particular including the full dependence of these observables on centrality, will provide more insights into the properties of the system – such as initial velocities, the equation of state and the fluid viscosity – and strongly constrain the theoretical modelling of heavy-ion collisions. [35] The ALICE results were announced at the August 13 Quark Matter 2012 conference in Washington. ALICE has just begun to explore the temperature dependence of η/s and we anticipate many more in-depth ance between the jet and its recoiling partner (G Aad et flow-related measurements at the LHC that will constrain al.76 TeV indicate strong in-medium energy loss for charm and strange quarks that is an indication of the formation of the hot medium of QGP. Off-centre nuclear collisions. they measure the momentum distributions of the emitted particles. which consist of a charm quark and an anti-charm.[36] Energy Loss Studying quarkonium hadroproduction Quarkonia are bound states of heavy flavour quarks (charm or bottom) and their antiquarks. for example in the production of pions. The observation from ALICE is consistent In heavy-ion collisions at the LHC. With these measurelatter two experiments have shown a strong energy imbalments.[34] This temperature is about 38% higher than the previous record of about 4 trillion degrees. the ALICE collab. and bottomonia made of a bottom and an anti-bottom quark. in other words it tells us about how the yields of hadrons with high transverse momentum. D. The quark–gluon plasma produced by these experiments approximates the conditions in the universe that existed microseconds after the Big Bang.[33] getic partons. the η/s ratio is small. or more precisely. new features. the ratio of ion collisions at the LHC. the matter flows. the observations at the LHC show qualitatively liquid. The yields of these high-pT particles in The measured azimuthal distribution of particles in mo. the production the shear viscosity (η) to entropy (s) of the system. As at RHIC. ALICE has recently published tic flow. A correlation between the measured azimuthal momentum distribution of particles emitted from the decaying fireball and the initial spatial asymmetry can arise only from multiple interactions between the constituents Jet quenching was first observed at RHIC by measuring of the created matter. This phenomenon. is especially useful in the study of the QGP. transferring a substantial fraction of its energy to the medium in a way that is not recovered by the reconstruction of the jets. such as honey.[38] A basic process in QCD is the energy loss of a fast parton in a medium composed of colour charges. The amount of the radiated energy is proportional to the density of the medium and to the square of the path length travelled by the parton in the medium.2. with a finite impact parameter. The search for quarkonia suppression as a QGP signature started 25 years ago. A LARGE ION COLLIDER EXPERIMENT A perfect liquid at the LHC 33 the incoming nuclei. using the naturally occurring products As the temperature increases so does the colour screening (jets) of the hard scattering of quarks and gluons from resulting in greater suppression of the quarkonium states . The second Fourier coefficient (v2). The theory also shows that a parton traversing the medium will lose a fraction of its energy in emitting many soft (low energy) gluons.with reports from the ATLAS and CMS collaborations on oration found that the hot matter created in the collision direct evidence for parton energy loss within heavy-ion jets of behaves like a fluid with little friction. is particularly sensitive to the internal friction or the measurement of charged particles in central heavyviscosity of the fluid. 2010 and CMS collaboration 2011). “jet quenching”. Measuring the highest temperature on Earth In August 2012 ALICE scientists announced that their experiments produced quark–gluon plasma with temperature at around 5. create a strongly asymmetric “almond-shaped” fireball. The production of these partonic probes in hadronic collisions is well understood within perturbative QCD. The lower limit (almost zero viscosity). A “thick” However. in which there are many free colour charges.C. A highly energetic parton (a colour charge) probes the coloured medium rather like an X-ray probes ordinary matter. has large values of η/s. Instead. Theory also predicts that the energy loss depends on the flavour of the parton. However.proton–proton reactions. with η/s close to its collisions using fully reconstructed back-to-back[37] particles associated with hard parton scatterings. Two types of quarkonia have been extensively studied: charmonia.2. For a of high-pT hadrons at the LHC is strongly suppressed. hot and dense matter. good fluid such as water. the highest temperature mass achieved in any physical experiments thus far. called ellip. see[32] ). η/s. before the matter coalesced into atoms. The “melting” of quarkonia into the QGP manifests itself in the suppression of the quarkonium yields compared to the production without the presence of the QGP.central nucleus–nucleus collisions were found to be a facmentum space can be decomposed into Fourier coeffi. This imbalance is thought to arise because one of the jets traversed the the hydrodynamic features of the QGP even further. achieved in the 2010 experiments at the Brookhaven National Laboratory. The first ALICE results for charm hadrons in PbPb collisions at a centre-of-mass energy √sNN = 2.5 trillion degrees.tor of five lower than expected from the measurements in cients.Charm and anticharm quarks in the presence of the Quark Gluon Plasma. are not able to see each other any more and therefore they cannot form bound states.. experiments cannot measure the spatial dimensions of the interaction (except in special cases. which is related to its equation of state These particles are produced via fragmentation of enerand its thermodynamic transport properties. the biggest surprise came from the observation that this near-side ridge is accompanied by an essentially symmetrical away-side ridge. in which Quark Gluon Plasma is not formed. 3. This double ridge was revealed after the short-range correlations arising from jet fragmentation and resonance decays were suppressed by subtracting the correlation distribution measured for low-multiplicity events from the one for high-multiplicity events. Such an effect is likely to be related to a regeneration process occurring at the temperature boundary between the QGP and a hot gas of hadrons CHAPTER 2. in heavy-ion collisions. comes from the charmonium states. expected results were widely accompanied by unanticipated observations. Such an ordering in mass was observed in heavy-ion collisions. they melt in the QGP. has been measured in high-multiplicity pPb collisions. Similar long-range structures in heavy-ion collisions have been attributed to the collective flow of particles emitted from a thermalized system undergoing a collective hydrodynamic expansion. . Today there is a large amount of data available from RHIC and LHC on charmonium and bottomonium suppression and ALICE tries to distinguish between effects due to the formation of the QGP and those from cold nuclear matter effects. EXPERIMENTS the LHC revealed a completely unexpected double-ridge structure with so far unknown origin.) coefficients of a Fourier decomposition of the single-particle azimuthal distribution. more J/ψ mesons are detected by the ALICE experiment in Pb–Pb with respect to p–p. Whereas J/ψ production does not reveal any unexpected behaviour. the ALICE collaboration has extended the two-particle correlation analysis to identified particles.7) with respect to J/ψ. Among the expected results is the confirmation that proton–nucleus collisions provide an appropriate tool to study the partonic structure of cold nuclear matter in detail.[40] . ALICE records first proton-lead collisions at the LHC The analysis of the data from the p-Pb collisions at The first pPb measurement campaign. Is this a hint of effects of the medium? Indeed. but with a much larger amplitude ([39] ). forming a ridge-like structure observed in high-multiplicity pp collisions. The proton–lead (pPb) collisions in 2013. Therefore. where it was interpreted to arise from a common radial boost – the so-called radial flow – coupled to the anisotropy in momentum space.34 as it is more difficult for charm – anticharm or bottom – antibottom to form new bound states. A surprising near-side. and a balancing mechanism of recombination of quarkonia may appear as we move to higher energies. two years after its heavy-ion collisions opened a new chapter in exploration of the properties of the deconfined. checking for a potential mass ordering of the v2 harmonic coefficients. the production of the heavier and lessDouble-ridge structure in p-Pb collisions bound (2S) state indicates a strong suppression (0. such a suppression has been interpreted as a sequential melting of quarkonia states. was also found in high-multiplicity pPb collisions. However. opposite in azimuth (CERN Courier March 2013 p6). Continuing the surprises. as states with different masses have different sizes and are expected to be screened and dissociated at different temperatures. when compared with the observations from lower energies. September 2013). While a similar suppression is observed at LHC energies for peripheral collisions. To test the possible presence of collective phenomena further.as the collision energy increases so does the number of charm-anticharm quarks that can form bound states. eventually. similar to the one observed in mid-central PbPb collisions (CERN Courier. This suggests that the observed suppression in proton-nucleus collisions (pA) is due to cold nuclear matter effects. a clear particle-mass ordering. the formation of QGP. when moving towards more head-on collisions – as quantified by the increasing number of nucleons in the lead nuclei participating in the interaction – the suppression no longer increases. long-range (elongated in pseudorapidity) correlation.. However . when compared with pp collisions. depending on their binding energy and the temperature of the QGP created in these collisions. The surprises have come from the similarity of several observables between pPb and PbPb collisions. which hint at the existence of collective phenomena in pPb collisions with high particle multiplicity and. This anisotropy can be characterized by means of the vn (n = 2. The results from the first ALICE run are rather striking. At very high temperatures no quarkonium states are expected to survive. The final surprise. so far.5–0. Grasping the wealth of experimental results requires understanding the medium modification of quarkonia and disentangling hot and coldmatter effects. chirally symmetrical state of the QGP. Quarkonium sequential suppression is therefore considered as a QGP thermometer. The suppression of charmonium states was also observed in proton-lead collisions at the LHC. despite the higher temperatures attained in the nuclear collisions at the LHC.. 27 June 2000 [29] ALICE Data Acquisition [30] ALICE presents first results at 7 TeV CERN Courier.2. CERN Courier. 18 December 2012 [4] ALICE New Kid on the block CERN Courier. LS2. 08 July 2008 [21] ALICE revolutionizes TOF systems CERN Courier. 05 December 2012 sions at the top LHC energy of 5.[9] LHC begins physics with lead ions CERN Courier. when the collaboration looks forward to heavy-ion colli. an entirely new rail system and cradle will be installed to support the three PHOS [11] First lead-ion collisions in the LHC Symmetry Magazine. This new subdetector will be installed on the bottom of the solenoid mag[10] First ions for ALICE and rings for LHCb CERN Courier. The installation of five modules of the TRD will follow and so complete this complex detec.2. 17 May 2013 [23] ALICE crystals arrive at CERN CERN Courier. 06 December 2006 the 18 ALICE subdetectors underwent major improvements during LS1 while the computers and discs of the [14] The Inner Tracking System arrives at the heart of ALICE online systems are replaced. 25 October 2011 [22] PHOS commissioning during LS1 ALICE matters. which consists of 18 units. 03 May 2011 [6] Experiments Revisit the Quark-Gluon Plasma CERN Courier. all of [13] ALICE forges ahead with detector installation CERN Courier.[16] Upgrade of the ALICE ITS ALICE Matters. 07 June 2010 [5] ALICE Experiment approved CERN timeline [31] ALICE Collaboration measures the size of the fireball in heav-ion collisions CERN Courier. CERN Courier. followed by upgrades of the CERN Courier. net. which currently houses three modules of the photon 30 October 2009 spectrometer (PHOS). 13 July 2012 (DCAL). 05 September 2004 [26] ALICE Forward Detectors [27] ALICE Dimuon Spectrometer [28] Meeting the ALICE data challenge CERN Courier.[12] Particle identification in ALICE boosts QGP studies CERN Courier.5 TeV/nucleon at luminosities in excess of 1027 Hz/cm2 . Moreover. In addition to these mainstream detector activities. currently scheduled for 2018. an extension of the existing EMCAL system that adds 60° of azimuthal acceptance opposite the exist. 19 September 2008 [18] Time Projection Chamber [19] Transition Radiation Detector [20] Time flies for ALICE CERN Courier.8 References [1] ALICE through the phase transition. the time-projection chamber will be upgraded with gaseous electron-multiplier (GEM) detectors for continuous read-out and the use of new microelectronics. which together weigh more than 100 tones. 30 October 2000 [2] Interview with Krishna Rajacopal.2. The ALICE collaboration has plans for a major upgrade during the next long shutdown. 08 November 2010 modules and eight DCAL modules. [15] Pixels make for perfect particle tracking in ALICE CERN All of these efforts will ensure that ALICE is in good Courier.2. 30 November 2010 ing 120° of the EMCAL’s acceptance. and all of the other subdetectors and the online systems will prepare for a 100-fold increase in the number of events written to tape.7 Future Plans 35 [7] RHIC starts producing data CERN Courier. preparing technical design reports for submission later this year. 2. 04 June 2007 operating systems and online software. 25 January 2012 . 10 October 2000 The main upgrade activity on ALICE during LHC’s Long [8] Interview with CERN’s theorist Urs Wiedemann ALICE Shutdown 1 was the installation of the dijet calorimeter Matters. 22 May 2013 [25] Indian detector stars at Brookhaven CERN Courier. A LARGE ION COLLIDER EXPERIMENT 2. 26 February 2001 [32] ALICE enters new territory in heavy-ion collisions. 30 September 2002 [24] First jet measurements with ALICE CERN Courier. ALICE Matters. the LS1 efforts go beyond the hardware activities that are currently under way. 08 July 2008 shape for the three-year LHC running period after LS1. With only five years to go before this major upgrade. ALICE Matters. 15 April 2013 [3] Interview with Johan Rafelski. the ALICE collaboration is also busy on this front. [17] ALICE Time Projection Chamber However. Then the entire silicon tracker will be replaced by a monolithicpixel tracker system. 23 August 2012 tor system. Recountries. CMS. and officially funded by the CERN member .3S8002T. The ATLAS experiment was proposed in its current form in 1994. Nature newsblog.. (ALICE collaboration) (2008). 20 August 2013 [39] ALICE and ATLAS find intriguing double ridge in protonlead collisions CERN Courier.2.1 History [38] Studying Quarkonium hadroproduction with ALICE ALICE Matters. February 2014 2. 13 August 2012. Journal of Instrumentation 3 (8): S08002.Fabiola Gianotti. Aamodt et al.1088/17480221/3/08/S08002. Yahoo! News. and weighs about 7. general-purpose particle detector for the Large Hadron Collider. LHCf and MoEDAL) constructed at the Large Hadron Collider (LHC).Charlton. and also benefitted from the detector research and development that had been done for the Superconducting Supercollider. The ATLAS collaboration. Bibcode:2008JInst. “The ALICE experiment at the CERN LHC”. TOTEM. Lepton and Energy Measurements) and ASCOT (Apparatus with Super Conducting Toroids) collaborations merged their efforts to build a single.[3] The project was led for the first 15 years by trieved 15 August 2012 Peter Jenni and between 2009 and 2013 was headed by [35] Hot stuff: CERN physicists create record-breaking sub.3 ATLAS experiment “ATLAS” redirects here. it contains some 3000 km of cable. 25 January 2012 Scientist.[5] The design was a combination of the two previous experiments.36 CHAPTER 2. doi:10. It was one of the two LHC experiments intrieved 15 August 2012 volved in the discovery[4] of a particle consistent with the [36] LHC primordial matter is hottest stuff ever made. ATLAS logo Coordinates: 46°14′8″N 6°3′19″E / 46.000 tonnes.9 External links • Official ALICE Public Webpage at CERN • Interactive Timeline for ALICE 20th anniversary • ALICE section on US/LHC Website • Photography panorama of ALICE detector center • K.[2] The experiment is a collaboration involving [34] CERN scientists create the highest temperature mass huroughly 3. EXPERIMENTS ATLAS is 46 metres long. New Higgs boson in July 2012. (Full design documentation) 2. For other uses. 15 August 2012. Since 2013 it has been headed by David atomic soup.23556°N 6. Re. 25 metres in diameter. The experiment is designed to take advantage of the unprecedented energy available at the LHC and observe phenomena that involve highly massive particles which were not observable using earlier lower-energy accelerators.. was formed in 1992 when the proposed EAGLE (Experiment for Accurate Gamma. 14 August 2012. see Atlas (disambiguation). CERN Courier. [33] Hadron spectra probe nature of matter in Pb-Pb collisions. 31 May 2012 2.3. For the linear accelerator. the group of physicists who built and now run the detector.05528°E ATLAS (A Toroidal LHC ApparatuS)[1] is one of the seven particle detector experiments (ALICE. February 2013 [40] Is Cold nuclear matter really cold? CERN Courier. ATLAS. see Argonne Tandem Linear Accelerator System. LHCb. a particle accelerator at CERN (the European Organization for Nuclear Research) in Switzerland.000 physicists from over 175 institutions in 38 manity has ever seen. It might shed light on new theories of particle physics beyond the Standard Model. Retrieved 15 August 2012 [37] ALICE tracks charm energy loss CERN Courier. their properties. universities. will represent a “new generation” of particle accelerators. While the Standard Model predicts that quarks. when colliding beam operation at the LHC started. Rather than focusing on a particular physical process. These collisions were successparticles. This is intended to ensure that whatever form any new physical processes or particles might The first cyclotron. with detector components then being shipped to CERN and assembled in the ATLAS experiment pit from violation of “naturalness” most particle physicists believe it is possible that the Standard Model will break 2003. ever since. and neutrinos should exist. All the while LHC energy has been increasing: 900 GeV per beam at the end of 2009. However. If detected its first single beam events on 10 September of such beyond-the-Standard-Model physics is observed it [6] that year. ATLAS EXPERIMENT Fabiola Gianotti. for size comparison. duced. Most of curred at the LHC.2. Construction work began at individual institutions. countries in 1995. the first proton-proton collisions octo describe particle physics at higher energies. 3. Collider (LHC) collides two beams of protons together.000 GeV per beam. electrons. were 1 megaelectronvolt (MeV). Data taking was then interrupted for over is hoped that a new model. some of which are hoped to be light enough to fully registered in ATLAS. ATLAS will be able to detect them and measure tor.500 GeV ATLAS is designed to be a general-purpose detector. Since then. was built by Ernest O. Lawrence in 1931. After a Long Shutdown in 2013 and 2014 Collider interact in the center of the detector.2 Background ble range of signals. accelerators have designed based on a similar philosophy.000 GeV per When the proton beams produced by the Large Hadron beam in 2012. As accelerators have grown. which has been logging data be observed by ATLAS. a variety of different particles with a broad range of energies are prothe accelerator will increase to 7. . Due to this each proton carrying presently about 4 TeV of energy – enough energy to produce particles with masses up to roughly ten times greater than any particles currently known – assuming of course that such particles exist. Note the people in the background. of particle interactions available today is known as the At 27 kilometres in circumference. down at energies beyond the current energy frontier of Construction was completed in 2008 and the experiment about one teraelectronvolt (TeV) (set at the Tevatron). Construction was completed in 2008 and the experiment has been successfully collecting data since November 2009. and further institutions and physicists continue to join the collaboration even today. an early type of particle accelera.take. the grown enormously in the quest to produce new particles unique challenges of the Large Hadron Collider – its unof greater and greater mass.3. with a ra.3. With the important exception of the Higgs boson (which most probably has just been observed by the ATLAS and the CMS experiments). ATLAS is designed to measure the broadest possi2. at a relatively low injection energy the currently proposed theories predict new higher-mass of 450 GeV per beam.[7] all of the particles predicted by the model have been observed. the Large Hadron Standard Model of Particle Physics. Additional countries. project leader 2009-13 37 ATLAS experiment under construction in October 2004 in the experiment pit. Experiments at earlier colliders. can be developed November 2009. precedented energy and extremely high rate of collisions so too has the list of known particles that they might – require ATLAS to be larger and more complex than any be used to investigate. and laboratories joined in subsequent years. such as dius of just a few centimetres and a particle energy of the Tevatron and Large Electron-Positron Collider. which is identical to the Stana year due to an LHC magnet quench incident. When upgraded in 2014. the LHC with an energy seven million times that of the first accelerator. it does not explain why the masses of these particles are so very different. The most comprehensive model detector ever built. for the whole of 2010 and 2011 and finally 4. On 23 dard Model at energies thus far probed. for example. the new particle was indeed a Higgs boson. perhaps revealing inconsistencies that point to new physics. The layers are made up of detectors of different types. Physicists have now to pursue their measurements to determine if this Higgs particle corresponds indeed to the Standard Model Higgs boson or if it is part of a new physics scenario. shedding light on this problem.Kaluza–Klein theory.their discovery would certainly indicate that there was dated ATLAS and CMS results.In March 2013. ATLAS (together with CMS – its sister experi. The different traces that particles leave in each layer of the detector allow for effective particle identification and accurate measurements of energy and momentum.[9] The Higgs mechanism. have so far only been measured approximately. It is possible that new models of physics will introduce additional CP violation.[8] 2. ATLAS is the largest detector ever built at a particle collider. ATLAS may eventually measure the mass of the W boson twice as accurately as has previously been achieved. leaving as a signal one or more high-energy 5 sigma. With much greater energy and greater collision rates.[9] Current CP violation experiments. highly massive partibosons mass while leaving the photon massless. Modweak force and electromagnetism by giving the W and Z els of supersymmetry involve new. energies.Other hypothetical massive particles.tentially solve a number of problems in theoretical physics tary particles. allowing ATLAS to make much more precise measurements of its mass and interactions with other particles. the detectors attached to it must grow to effectively measure and stop higher-energy particles. the proton mass. In order to identify all particles produced at the interaction point where the particle beams collide.and stable heavy particles that are very unlikely to interact ment at the LHC) reported evidence for the existence of with ordinary matter. or 133 times quark jets and a large amount of “missing” momentum. each of which is designed to observe specific types of particles. like those in the tected by its possible decay into two photons and its de. or indirectly by measurements of the properties of B-mesons. in the light of the up. (LHCb. The theory is popular because it could pothe Higgs boson. In many cases these decay into high-energy quarks 4. The asymmetry between the behavior of matter and antimatter. and nuclear spins. One theory vestigate a missing piece of the Standard Model. Peter Higgs and François Englert were awarded the Nobel Prize in Physics.) As the energy of the particles produced by the accelerator increases.searching directly for new models of physics. momentum. charges. might leave a similar signature. Having analyzed two and a half times more data than was available for the discovery announcement in July. and this is the task of particle detectors. This new “Higgs-like” particle was de.3 Physics program Schematics. is hypothesized to give mass to elemen. giving rise to the differences between the and is present in almost all models of string theory. ATLAS is intended to investigate many different types of physics that might become detectable in the energetic collisions of the LHC. such as BaBar and Belle.[11] These measurements will provide indirect information on the details of the Standard Model. the confidence of observation has risen to 10 sigma. lifetime.[7] with a mass around 125 GeV. The stable particles would escape a particle consistent with the Higgs boson at the level of the detector. the that is the subject of much current research is broken suHiggs boson. is likely to be better suited to the latter). which includes persymmetry. is also being investigated. In 2013 two of the theoretical physicists who predicted the existence of the Standard Model Higgs boson. an LHC experiment dedicated to B-mesons. which is expected to have spin 0 and parity +. CERN announced that some kind of physics beyond the Standard Model. Particle detectors must be built to detect particles. while many others are possible clues for new physical theories. the LHC produces a tremendous number of top quarks. have not yet detected sufficient CP violation in the Standard Model to explain the lack of detectable antimatter in the universe. discovered at Fermilab in 1995. Perhaps the most exciting lines of investigation are those One of the most important goals of ATLAS was to in. 2012. (The role of each layer in the detector is discussed below. called Feynman diagrams show the main ways that the Standard Model Higgs boson can be produced from colliding protons at the LHC. On July cles. . particle detectors are usually designed in layers like an onion. While interesting phenomena may occur when protons collide it is not enough to just produce them.38 CHAPTER 2. known as CP violation. The experiments were also able to show that the properties of the particle as well as the ways it interacts with other particles were well-matched with those of a Higgs boson. EXPERIMENTS Particles that are produced in accelerators must also be observed. but cay to four leptons. their masses. Evidence supporting these models might either be detected directly by the production of new particles.[10] The properties of the top quark. Similar precision measurements will be made of other known particles. Some of these are confirmations or improved measurements of the Standard Model.3. tor has over 80 million readout channels.contains three concentric layers and three disks on each ters. each measuring 2 Each of these is in turn made of multiple layers.[17] The magnetic field surrounding the entire inner detector causes charged particles to curve. that micro black holes could be formed by the LHC. revealing detailed information about the types of particles and their momentum. the calorimeters measure the energy chips and other electronic components.3. Another challenge was the radiation to which the Pixel Detector is exposed because of its proximity to the interaction point. this may be a sign that the particles came from the decay of a hadron with a bottom The ATLAS detector consists of a series of ever-larger quark (see b-tagging). The starting points of the tracks yield useful information for identifying particles. The detecting material is detectors are complementary: the Inner Detector tracks 250 µm thick silicon. the direction of the curve reveals a particle’s charge and the degree of curvature reveals its momentum. The centimetres by 6 centimetres.[12] These would decay immediately by means of Hawking radiation.2 metres in length along the beam pipe. their presence is inferred by measuring a momentum imbalance among detected particles. there are roughly 47. Maintaining detector performance in the high radiation areas immediately surrounding the proton Some hypotheses involving large extra dimensions predict beams is a significant engineering challenge. For this to work.3. which is about Computer generated cut-away view of the ATLAS detector showing its various components Muon Spectrometer: (1) Monitored Drift Tube (2) Thin Gap Chamber Magnet system: (3) End-Cap Toroid Maget (4) Barrel Toroid Magnet Inner Detector: (5) Transition Radiation Tracker (6) Semi-Conductor Tracker (7) Pixel Detector Calorimeters: (8) Electromagnetic Calorimeter (9) Hadronic Calorimeter The only established stable particles that cannot be detected directly are neutrinos. The minute The two magnet systems bend charged particles in the In.4 Micro black holes 2. The ATLAS TRT (Transition Radiation Tracker) central section. assembled above ground and taking data from cosmic rays[15] in September 2005 The Inner Detector[16] begins a few centimetres from the proton beam axis. ATLAS EXPERIMENT 2. In total. the detector must be "hermetic". producing all particles in the Standard Model in Inner Detector equal numbers and leaving an unequivocal signature in the ATLAS detector. the proton beams from the LHC collide. Having such a large count created a considerable design and engineering challenge. requiring . allowing their close to the interaction point. The smallest unit of easily stopped particles. with 50% of the total readout channels of the whole experiment. The Inner Detector has three parts.[13] If this occurs. for example. into four major parts: the Inner Detector. concentric cylinders around the interaction point where which are explained below. extends to a radius of 1.[14] end-cap.pixel size is designed for extremely precise tracking very ner Detector and the Muon Spectrometer.000 pixels per module. if a group of tracks seem to originate from a point other than the original proton–proton collision. with a total of 1. Its basic function is to track charged particles by detecting their interaction with material at discrete points. meaning it must detect all non-neutrinos produced.3.2 metres. additional measurements of highly penetrating muons. and is 6. the Muon Spectrometer and the magnet systems.2. the outermost part of the Inner Detector. the primary studies of Higgs bosons and top quarks would in fact be looking at those produced by the black holes.[18] the innermost part of the detector. It can be divided The Pixel Detector. the calorime. Each module contains 16 readout particles precisely.744 modules.5 Components 39 no blind spots. the Pixel Detecmomenta to be measured. and the muon system makes that can be read out is a pixel (50 by 400 micrometres). each four millimetres in diameter and up to 144 centimetres long. The straws are held at about −1. Be. It has high precision. It is composed of four double layers of silicon strips. tween the straws. but it was necessary to reduce the cost of covering a larger volume and to have transition radiation detection capability. materials with widely varying indices of refraction cause ultra-relativistic charged particles to produce transition radiation and leave much stronger signals in some straws. The SCT is the most critical part of the inner detector for basic tracking in the plane perpendicular to the beam. The uncertainty of track position measurements (position resolution) is about 200 micrometres. The Transition Radiation Tracker (TRT). Xenon gas is used to increase the number of straws with strong signals. calorimeter. Calorimeters The extended barrel section of the hadronic calorimeter. which include charged particles and photons. making coverage of a larger area practical. both in the amount of energy absorbed and in the precise location of the energy deposited. inferring the energy of the original particle from this measurement. and because particles of a particular energy have a higher speed the lighter they are. Each strip measures 80 micrometres by 12 centimetres. that allow the path of the particle to be determined. positrons.waiting to be inserted in late February 2006. There are two basic calorimeter systems: an inner electromagnetic calorimeter and an outer hadronic calorimeter. is a combination of a straw tracker and a transition radiation detector. narrow strips rather than small pixels. The electromagnetic (EM) calorimeter absorbs energy from particles that interact electromagnetically. that is. The detecting elements are drift tubes (straws). The wires with signals create a pattern of 'hit' straws One of the sections of the extensions of the hadronic calorimeter. driving the negative ions to a fine wire down the centre of each straw. since it measures particles over a much larger area than the Pixel Detector. Each straw is filled with gas that becomes ionized when a charged particle passes through. waiting to be moved inside the toroid magnets. EXPERIMENTS that all components be radiation hardened in order to continue operating after significant exposures. The TRT has about 298. Since the amount of transition radiation is greatest for highly relativistic particles (those with a speed very near the speed of light). producing a current pulse (signal) in the wire.3 million readout channels and a total area of 61 September 2005: The main barrel section of the ATLAS hadronic square meters. The Semi-Conductor Tracker (SCT) is the middle component of the inner detector. with more sampled points and roughly equal (albeit one-dimensional) accuracy.500 V. It is similar in concept and function to the Pixel Detector but with long. The barrel EM calorimeter has accor- . and has 6. particle paths with many very strong signals can be identified as belonging to the lightest charged particles: electrons and their antiparticles. The calorimeters are situated outside the solenoidal magnet that surrounds the Inner Detector.025 radians. the outermost component of the inner detector.000 straws in total. This is not as precise as those for the other two detectors. The angle between the particle’s trajectory and the detector’s beam axis (or more precisely the pseudorapidity) and its angle within the perpendicular plane are both measured to within roughly 0.40 CHAPTER 2. they absorb energy in high-density metal and periodically sample the shape of the resulting particle shower. Their purpose is to measure the energy from particles by absorbing it.[19] Both are sampling calorimeters. and a much larger volume. the force on particles of different momenta is equal. with scintillating tiles that sample the energy deposited. momentum is not linear proportional to veloc- . albeit with a different magnetic field configuration. as it looked in February 2007. standalone. The far-forward sections of the hadronic calorimeter are contained within the forward EM calorimeter’s cryostat.25 m close to the calorimeters out to the full radius of the detector (11 m). (In the theory of relativity. these particles are primarily hadrons. which first go through all the other elements of the detector before reaching the muon spectrometer. Part of the ATLAS detector.2. The extent of this sub-detector starts at a radius of 4. with liquid argon as the sampling material. in September 2005. the momentum of 100 GeV muons with 3% accuracy and of 1 TeV muons with 10% accuracy. and because the total energy of particles in an event could not be measured if the muons were ignored.1 radians only). Since all particles produced in the LHC’s proton collisions are traveling at very close to the speed of light. but do interact via the strong force. It functions similarly to the Inner Detector. the instrument is large and comprises a huge amount of construction material: the main part of the calorimeter – the tile calorimeter – is 8 metres in diameter and covers 12 The ends of four of the eight ATLAS toroid magnets. Magnet system The ATLAS detector uses two large superconducting magnet systems to bend charged particles so that their momenta can be measured. It was designed to measure.000 square meters. and use liquid argon as well. metres along the beam axis. The hadron calorimeter absorbs energy from particles that pass through the EM calorimeter. and a cryostat is required around the EM calorimeter to keep it sufficiently cool. lower spatial precision.[14] Its tremendous size is required to accurately measure the momentum of muons. looking down from about 90 metres above. Muon Spectrometer The Muon Spectrometer is an extremely large tracking system. It is less precise. (2) a set of 1200 chambers measuring with high spatial precision the tracks of the outgoing muons.3. consisting of three parts: (1) a magnetic field provided by three toroidal magnets. It has roughly one million readout channels. and its layers of detectors have a total area of 12. Many of the features of the calorimeter are chosen for their cost-effectiveness. which is proportional to velocity. It was vital to go to the lengths of putting together such a large piece of equipment because a number of interesting physical processes can only be observed if one or more muons are detected. while copper and tungsten are used as absorbers. both in energy magnitude and in the localization (within about 0.[10] The energyabsorbing material is steel. It also serves the function of simply identifying muons – very few particles of other types are expected to pass through the calorimeters and subsequently leave signals in the Muon Spectrometer. ATLAS EXPERIMENT 41 dion shaped electrodes and the energy-absorbing materials are lead and stainless steel. (3) a set of triggering chambers with accurate time-resolution. This bending is due to the Lorentz force. with muons curving so that their momentum can be measured. 4 July 2012.ch/fact-sheets-1-view.6 gigajoules of energy. Ethernet. ATLAS. 2. There are three trigger levels. signing the LHC experiments evaluated several such netThe outer toroidal magnetic field is produced by eight works. objects. photons. Offline event reconstruction is performed on all permanently stored events. Retrieved 2008-09-13. 4 July 2012. however.. field allows even very energetic particles to curve enough for their momentum to be determined. This amount of data still requires over 100 of disk space per second – at least a petabyte surrounding the Inner Detector. the most interesting events to retain for detailed analysis. (ATLAS Collaboration) (2008).[22] The trigger system[23] uses simple information to identify.) Thus high-momentum particles curve very little. and leptons. prior to the first proton collisions. loop repeatedly in the field and most likely not be mea. doi:10. G. Bibcode:2008JInst. Since such a bus architecture cannot keep roughly 400 MeV will be curved so strongly that they will up with the data requirements of the LHC experiments.000 events per second. all situated outside the calorimeters and within the muon system. Particles with momenta below or FASTBUS. such as jets. this energy is very small compared to the point-to-point links and switching networks. other two run primarily on a large computer cluster near the detector. turning the pattern of signals from the detector into physics objects. [7] “CERN experiments observe particle consistent with long-sought Higgs boson”. because a solenoid magnet of sufficient size would be prohibitively expensive to build.42 CHAPTER 2. After the third-level trigger has been applied. “The ATLAS Experiment at the CERN Large Hadron Collider”. This produces a total of 1 petabyte of raw data per second. .6 MB). including Asynchronous Transfer Mode.[20] This magnetic field extends in an area 26 metres long and 20 metres in diameter. The first is based in electronics on the detector while the [4] “CERN experiments observe particle consistent with long-sought Higgs boson”.8 Notes [1] Aad.[20] This high magnetic megabytes[24] each year. Retrieved 2007-02-25.all data acquisition system proposals rely on high-speed sured. provided performance characteristics very close to its design values.3S8003A.3.html [3] “What is ATLAS?".3.3. EXPERIMENTS ity at such speeds.1088/17480221/3/08/S08003. Retrieved 4 July 2012. CERN.atlas. Atlas. in real time. Its magnetic field is not uniform. and IEEE very large air-core superconducting barrel loops and two Coherent Interface. Retrieved 2013-10-27. These detectors are located in the LHC tunnel far away from the interaction point.[21] 2. The basic idea is to measure elastic scattering at very small angles in order to produce better measurements of the absolute luminosity at the ATLAS interaction point. Journal of Instrumentation 3 (8): S08003. Grid computing is being extensively used for event reconstruction.[25] 1355 (SpaceWire). multiplied by 40 million beam crossings per second in the center of the detector. a few hundred events remain to be stored for furThe inner solenoid produces a two tesla magnetic field ther analysis. Detector performance The software for these tasks has been under development for many years. People deseveral TeV of energy released in each proton collision. CERN Archive. et al. The first-level trigger selects about 100. It varies between 2 and 8 Teslameters. Retrieved 2013-10-27.ch. 2. CERN. the amount of curvature can be quantified and the particle momentum can be determined from this value. [2] http://www.6 Data systems and analysis The detector generates unmanageably large amounts of raw data: about 25 megabytes per event (raw. August 2008. end-caps air toroidal magnets.7 See also Forward detectors The ATLAS detector is complemented by a set of detectors in the very forward region. [6] “First beam and first events in ATLAS”.. while low-momentum particles curve significantly. The detectors collected millions of cosmic Individuals and groups within the collaboration are writrays during the magnet repairs which took place between ing their own code to perform further analysis of these fall 2008 and fall 2009. and its nearly Earlier particle detector read-out and event detection sysuniform direction and strength allow measurements to tems were based parallel shared buses such as VMEbus be made very precisely. searching the patterns of detected particles for The detector operated with close to 100% efficiency and particular physical models or hypothetical particles.. and it stores 1. Scalable Fibre Channel. [5] “ATLAS Collaboration records”. and will continue to be refined even now The installation of all the above detectors was finished in that the experiment is collecting data. allowing the parallel use of university and laboratory computer networks throughout the world for the CPU-intensive task of reducing large quantities of raw data into a form suitable for physics analysis. zero suppression reduces this to 1. V. Bibcode:2010JHEP. Bibcode:2005EPJC.nima.. V.28. Bibcode:2006ITNS.3. “Study of Black Holes with the ATLAS detector at the LHC”. Krasnikov. 2006-11-20.53. 1994. A. 2. Ingenia magazine.R.114.1016/j. “The ATLAS pixel detector”. ATLAS Technical Proposal. 1994. CERN. CERN. G Aad et al. “Alignment of the ATLAS inner detector tracking system”.41.1016/j. Accelerators.2009. P. [23] D.1134/1. S. Retrieved on 2007-04-10 • N.A.2006.06.. V. Bibcode:2008JInst.9 References • ATLAS Technical Proposal. Spectrometers. CERN. Bibcode:1997PPN. [20] “Magnet system”. ATLAS Technical Proposal.. 2.nima.3. Sabetfakhri and B. Section A. et al. A. Scannicchio (2010).953049. Webber (2005).2. [13] J. Journal of High Energy Physics 5 (5): 053.617. Yamamura.10 External links • Official ATLAS Public Webpage at CERN (The “award winning ATLAS movie” is a very good general introduction!) • Official ATLAS Collaboration Webpage at CERN (Lots of technical and logistical information) • ATLAS Cavern Webcams • Time lapse video of the assembly • ATLAS section from US/LHC Website • New York Times article on LHC and experiments • United States Department of Energy article on ATLAS • Large Hadron Collider Project Director Dr Lyn Evans CBE on the engineering behind the ATLAS experiment. “Physics at LHC”. Nuclear Instruments and Methods in Physics Research. United States Department of Energy Research News. CERN.871506.1140/epjcd/s2005-02-008-x..28. “Readiness of the ATLAS detector: Performance with the first beam and cosmic data”. European Physical Journal C 41 (s2): 19–33. 1994.. CERN. G.. Section A. F.306S. Detectors and Associated Equipment 617 (1-3): 568–570. doi:10.. arXiv:hep-ph/0411095..2009.. Retrieved 2008-08-26. 1994.3S8003T. Asai. [15] F.. Parker.. (2008-0814). Archived from the original on 28 February 2007.J. doi:10. doi:10. Accelerators. [22] “Detector Description”.. “Physics at LHC”.1732H. 1. doi:10. ATLAS Technical Proposal. June 2008 • The ATLAS Collaboration. Palmer. [18] Hugging. doi:10.1088/1126-6708/2005/05/053. Retrieved on 2007-04-10 • ATLAS Detector and Physics Performance Technical Design Report. [24] “The sensitive giant”.053H. arXiv:hepph/9703204.2009.09. Performance and Application in High Energy Physics”.M. “The ATLAS Experiment at the CERN Large Hadron Collider”. Bibcode:1997PPN.568M. M.. V.1134/1. Nuclear Instruments and Methods in Physics Research. 1994. ATLAS EXPERIMENT 43 [8] “World’s largest superconducting magnet switches on” (Press release). Bibcode:2010NIMPA. [9] “Introduction and Overview”. M. [19] “Calorimetry”.19T. Harris. Richardson.953049.. “Performance of the ATLAS Detector using First Collision Data”... [14] “Overall detector concept”. Section A. doi:10. Matveev (September 1997). March 2004. p. ATLAS Technical Proposal.617. Tanaka.. CERN: The Atlas Experiment. CERN. (2006). Physics of Particles and Nuclei 28 (5): 441–470.nima. “The IEEE 1355 Standard: Developments.. “ATLAS Trigger and Data Acquisition: Capabilities and commissioning”. Retrieved 2007-03-03. [21] Aad.08.1088/1748-0221/3/08/S08003. Bibcode:2005JHEP. Accelerators. ATLAS Technical Proposal. doi:10. Matveev (September 1997). Spectrometers.. Journal of Instrumentation 3 (S08003): S08003.05. [17] “Inner detector”. (Full design documentation) • LEGO model of ATLAS. Physics of Particles and Nuclei 28 (5): 441–470..09.. [10] N..101. arXiv:physics/0412138.617. J. 1994. Detectors and Associated Equipment 617 (1/3): 306. Nuclear Instruments and Methods in Physics Research. [25] Stefan Haas. arXiv:hep-ph/9703204.1109/TNS. Bibcode:2010NIMPA.056A. Detectors and Associated Equipment 617 (1/3): 48.441K. arXiv:hep-ph/0411022... Kanzaki (2005). [16] Regina Moles-Valls (2010). doi:10. [12] C.1007/JHEP09(2010)056. ATLAS Technical Proposal. “Exploring higher dimensional black holes at the Large Hadron Collider”. doi:10. 1998.. Spectrometers.1016/j. A. by an ATLAS-scientist at the Niels Bohr Institute .48P.. Krasnikov.068.3. Pastore (2010). arXiv:1005. CERN.5254.. Bibcode:2010NIMPA. (ATLAS Collaboration) (2010). CERN: The Atlas Experiment. T. doi:10. IEEE Transactions on Nuclear Science 53 (6): 1732.A. [11] “Top-Quark Physics”.441K. JHEP 1009 (9): 056. View of the CMS endcap through the barrel sections. The magnetic field is confined by a steel 'yoke' that forms the bulk of the detector’s weight of 12 500 tonnes. In July 2012. It contains subsystems which are designed to measure the energy and momentum of photons. it was constructed on the surface. the lack of any particle see the Technical Design Report. EXPERIMENTS • Padilla. which are inside the return yoke of the magnet. the particle resulting from the Higgs mechanism which provides an explanation for the masses 2.[1] Approximately 3.2 Physics goals The main goals of the experiment are: • to explore physics at the TeV scale • to study the properties of the recently found Higgs boson • to look for evidence of physics beyond the standard model. The Compact Muon Solenoid (CMS) experiment is one of two large general-purpose particle physics detectors built on the Large Hadron Collider (LHC) at CERN in Switzerland and France. at the other side of the LHC ring is designed with similar goals in mind. CMS and ATLAS uses different technical solutions and design of its detector magnet system to achieve the goals. capable of studying many aspects of proton collisions at 8TeV. Sixty Symbols. Outside the magnet are the large muon detectors. and precision tests of.44 CHAPTER 2. and other products of the collisions. muons.[2] It is located in an underground cavern at Cessy in France.For full technical details about the CMS detector. Universe. CMS tentatively discovered the Higgs Boson through decay mechanisms. a number of questions remain unanswered.000 tonnes.1 Background Recent collider experiments such as the now-dismantled Large Electron-Positron Collider at CERN and the (as of October 2011) recently closed Tevatron at Fermilab have provided remarkable insights into. The tracker and the calorimetry are compact enough to fit inside the CMS Solenoid which generates a powerful magnetic field of 3.4. “ATLAS at the Large physics explanation for dark matter and the reasons for Hadron Collider”.3 Detector summary CMS is designed as a general-purpose detector.4 Compact Muon Solenoid Coordinates: 6. The ATLAS experiment. extra dimensions. The goal of CMS experiment is to investigate a wide range of physics. just across the border from Geneva.4. electrons. and weighs about 14.4 CMS by layers of elementary particles. The CMS detector is built around a huge solenoid magnet. 2.07694°E 46°18′34″N 6°4′37″E / 46. like the other giant detectors of the LHC experiments. including the search for the Higgs boson. and particles that could make up dark matter. Surrounding it is a scintillating crystal electromagnetic calorimeter. and the two experiments are designed to complement each other both to extend reach and to provide corroboration of findings. A principal concern is the lack of any direct evidence for the Higgs boson. 2. The innermost layer is a silicon-based tracker. Brady Haran for the imbalance of matter and antimatter observed in the the University of Nottingham. which is itself surrounded with a sampling calorimeter for hadrons. Antonio (Tony). about 100 000 times that of the Earth. form the CMS collaboration who built and now operate the detector. . before being lowered underground in 15 sections and reassembled. along with ATLAS.800 people. the center-of-mass energy of the LHC particle accelerator.4.4. This takes the form of a cylindrical coil of superconducting cable that generates a magnetic field of 4 teslas. 15 metres in diameter. 2.30944°N 2. please dard Model at high energies. The ladder to the lower right gives an impression of scale. the Standard Model of Particle Physics.6 metres long. representing 199 scientific institutes and 43 countries. CMS is 21. or extra dimensions • to study aspects of heavy ion collisions. An unusual feature of the CMS detector is that instead of being built in-situ underground. However. Other questions include uncertainties in the mathematical behaviour of the Stan.8 T. such as supersymmetry. with 75 million separate electronic read-out channels: in the pixel detector there are some 6000 connections per square centimetre. although the number of be lightweight so as to disturb the particle as little as poscollisions per second is only 31. The collisions occur at is also the inner most layer of the detector and so receives a centre of mass energy of 8 TeV. The CMS tracker records the paths taken by charged particles by finding their positions at a number of key points. This is the point in the centre of the detector at which proton-proton collisions occur between the two counterrotating beams of the LHC. scattering events are initiated by a single quark or gluon from each proton. There are 9. The inter. During full luminosity collisions the occupancy of the pixel layers per event is expected to be 0. due to both fewer proton bunches in each beam and fewer protons per bunch. The reduced bunch frequency does allow the crossing angle to be reduced to zero however.1%. followed by the remaining six layers of 25 cm × 180 μm strips. At collision each beam has a radius of 17 μm and the crossing angle between the beams is 285 μrad. and so the actual energy involved in each collision will be lower as the total centre of mass energy is shared by these quarks and gluons (determined by the parton distribution functions). The CMS tracker is made entirely of silicon: the pixels. The first test which ran in September 2008 was expected to operate at a lower collision energy of 10 TeV but this was prevented by the 19 September 2008 shutdown. It does this by taking position measurements so acthe beam as injector magnets are activated and deacti. the more curved the path.1 m. COMPACT MUON SOLENOID 45 A slice of the CMS detector. a fraction of the width of a human hair. the less momentum the particle had. as bunches are far enough spaced to prevent secondary collisions in the experimental beampipe.15×1011 protons. and 1– 2% in the strip layers. at the very core of the detector and dealing with the highest intensity of particles. Each measurement is accuAt full luminosity each collision will produce an average rate to 10 µm. But. This part of the detector is the world’s largest silicon . The innermost three layers (up to 11 cm radius) consist of 100×150 μm pixels. The CMS silicon tracker consists of 13 layers in the central region and 14 layers in the endcaps. contain 2.6 million due to gaps in sible. the als were therefore carefully chosen to resist radiation. The tracker can reconstruct the paths of high-energy muons.6 million strip channels in total.curate that tracks can be reliably reconstructed using just vated. The interaction point The silicon strip tracker of CMS.808 bunches of 1. and the silicon microstrip detectors that surround it.2. When at this target level. The next four layers (up to 55 cm radius) consist of 10 cm × 180 μm silicon strips. electrons and hadrons (particles made up of quarks) as well as see tracks coming from the decay of very short-lived particles such as beauty or “b quarks” that will be used to study the differences between matter and At full design luminosity each of the two LHC beams will antimatter. Layer 1 – The tracker Momentum of particles is crucial in helping us to build up a picture of events at the heart of the collision. At each end of the detector magnets focus the beams into the interaction point. The tracker employs sensors covering an area the size of a tennis court.The tracker needs to record particle paths accurately yet val between crossings is 25 ns. One method to calculate the momentum of a particle is to track its path through a magnetic field. 66 million in total. the LHC will have a significantly reduced luminosity. It of 20 proton-proton interactions. a few measurement points. out to a radius of 1. it is worth noting the highest volume of particles: the construction materi[3] that for studies of physics at the electroweak scale.4. As particles travel through the tracker the pixels and microstrips produce tiny electric signals that are amplified and detected. The expected SLHC upgrade will increase the number of interactions to the point where over-occupancy may significantly reduce trackfinding effectiveness. any circuit at CERN. with a 4 Tesla magnetic field that is 100. with 80% of light yield within one crossing time (25 ns). Its The inductance of the magnet is 14 Η and the nominal purpose is to aid in pion-photon discrimination. EXPERIMENTS detector. These allow CMS to distinguish between single high-energy photons (often signs of exciting physics) and the less interesting close pairs of low-energy photons.[4] Layer 2 – The Electromagnetic Calorimeter The Electromagnetic Calorimeter (ECAL) is designed to measure with high accuracy the energies of electrons and photons.0) is instrumented by the Hadronic Forward (HF) detector. but with a touch of oxygen in this crystalline form it is highly transparent and scintillates when electrons and photons pass through it.160 A. giving a total stored energy of 2. For extra spatial precision. They are set in a matrix of carbon fibre to keep them optically isolated. fast and fairly compact detector.500 A. and has a rapid light yield. short. consisting of two layers of lead interleaved with two layers of silicon strip detectors. and its refrigerated superconducting niobiumtitanium coils were originally intended to produce a 4 T magnetic field.46 CHAPTER 2. more momentum a particle has the less its path is curved . The flat ECAL endcaps seal off the barrel at either end and are made up of almost 15.[5] Layer 4 – The magnet The CMS magnet is the central device around which the experiment is built.[6] At the endcaps the ECAL inner surface is covered by the preshower subdetector. well-defined photon bursts that allow for a precise. The brass used in the endcaps of the HCAL used to be Russian artillery shells. each weighing around three tonnes and containing 1700 crystals.200 crystals formed into 36 “supermodules”.8 T instead of the full design strength in order to maximize longevity. ideal for stopping high energy particles. pions and kaons). This allows the charge/mass ratio of particles to be determined from the curved track that they follow in the magnetic field. Lead tungstate crystal is made primarily of metal and is heavier than stainless steel. The crystals used have a front size of 22 mm × 22 mm and a depth of 230 mm.66 GJ. This is balanced however by a relatively low light yield of 30 photons per MeV of incident energy. The high pseudorapidity region (3.8 T is interacting. The circuit resistance (essentially just The Hadron Calorimeter (HCAL) measures the energy the cables from the power converter to the cryostat) has of hadrons. It is 13 m long and 6 m in diameter. Located 11 m either side of the interaction point. The out via wavelength-shifting fibres by hybrid photodiodes. This is an extremely dense but optically clear material. The ECAL. 18. There are dump circuits to safely dissipate this energy should Layer 3 – The Hadronic Calorimeter the magnet quench. These high-density crystals produce light in fast. The operating field was scaled down to 3. giving a stored energy of 2.000 times stronger than the Earth’s. The HCAL consists of layers of dense material (brass or The job of the big magnet is to bend the paths of particles steel) interleaved with tiles of plastic scintillators. current for 4 T is 19. Additionally of nearly 39 hours. The cylindrical “barrel” consists of 61. CMS has a large solenoid magnet. this uses a slightly different technology of steel absorbers and quartz fibres for readout.3 GJ. designed to allow better separation of particles in the congested forward region. It has 205 m2 of silicon sensors (approximately the area of a tennis court) comprising 76 million channels. the ECAL also contains preshower detectors that sit in front of the endcaps. made up of a barrel section and two ”endcaps”. The operating current for 3. Half of the Hadron Calorimeter This combination was determined to allow the maximum amount of absorbing material inside of the magnet coil.1 mΩ which leads to a circuit time constant ample protons. PbWO4 . read emerging from high-energy collisions in the LHC. It has a radiation length of χ0 = 0. uncharged particles such as neutrinos. The HF is also used to measure the relative online luminosity system in CMS.a value of 0. This means it produces light in proportion to the particle’s energy. equivalent to about half-a-tonne of TNT. and backed by silicon avalanche photodiodes for readout.000 further crystals. particles made of quarks and gluons (for ex. neutrons. forms a layer between the tracker and the HCAL. The ECAL is constructed from crystals of lead tungstate.89 cm. This is the longest time constant of it provides indirect measurement of the presence of non.0 < |η| < 5. Each DT chamber. • A part of the Magnet Yoke. chambers to detect muons are placed at the very edge of the experiment where they are the only particles likely to register a signal. one of the clearest “signatures” of the Higgs Boson is its decay into four muons. which is then used by the trigger to make immediate decisions about whether the data are worth keeping. electrons are knocked out of gas atoms. CMS began with the aim of having the strongest magnet possible because a higher strength field bends paths more and. detecting muons is one of CMS’s most important tasks. CSCs consist of arrays of positively-charged “anode” wires crossed with negatively-charged copper “cathode” strips within a gas volume. The DTs are used for precise trajectory measurements in the central barrel region. on the yellow frame) waits to be inserted into the superconducting magnet (the silver cylinder in the centre of the red magnet yoke). also inducing a charge pulse in the strips. Each CSC module contains six layers making it able to accurately identify muons and match their tracks to those in the tracker. in the different layers. the closely spaced wires make the CSCs fast detectors suitable for triggering. In addition to providing precise space and time information.4.5m in size. Because the strips and the wires are perpendicular. Muons are charged particles that are just like electrons and positrons. RPCs consist of two parallel plates. Each 4-cm-wide tube contains a stretched wire within a gas volume.5 Collecting and collating the data Pattern recognition New particles discovered in CMS will be typically unstable and rapidly transform into a cascade of lighter. and must be very strong itself to withstand the forces of its own magnetic field. The drift tube (DT) system measures muon positions in the barrel part of the detector. this allows accurate measurement of the momentum of even high-energy particles. they knock electrons off the gas atoms. on average 2m x 2. which flock to the anode wires creating an avalanche of electrons. a positively-charged anode and a negatively-charged cathode. The tracker and calorimeter detectors (ECAL and HCAL) fit snugly inside the magnet coil whilst the muon detectors are interleaved with a 12-sided iron structure that surrounds the magnet coils and contains and guides the field. Cathode strip chambers (CSC) are used in the endcap disks where the magnetic field is uneven and particle rates are high. Positive ions move away from the wire and towards the copper cathode. Resistive plate chambers (RPC) are fast gaseous detectors that provide a muon trigger system parallel with those of the DTs and CSCs. the wires are going into the page) as well as by calculating the muon’s original distance away from the wire (shown here as horizontal distance and calculated by multiplying the speed of an electron in the tube by the time taken) DTs give two coordinates for the muon’s position.4. CMS uses three types of detector: drift tubes (DT). The RPCs provide a fast signal when a muon passes through the muon detector. Therefore. Particles travelling through CMS leave behind characteristic patterns. unlike most particles they are not stopped by any of CMS’s calorimeters. but are 200 times more massive. The enormous magnet also provides most of the experiment’s structural support. combined with high-precision position measurements in the tracker and muon detectors. allowing them . Made up of three layers this “return yoke” reaches out 14 metres in diameter and also acts as a filter. each with up to 60 tubes: the middle group measures the coordinate along the direction parallel to the beam and the two outside groups measure the perpendicular coordinate. The pattern of hit strips gives a quick measure of the muon momentum. allowing through only muons and weakly interacting particles such as neutrinos. Layer 5 – The muon detectors and return yoke As the name “Compact Muon Solenoid” suggests. 2. both made of a very high resistivity plastic material and separated by a gas volume. or ‘signatures’. consists of 12 aluminium layers. When a muon passes through the chamber. • The Hadron Calorimeter Barrel (in the foreground. which are instead picked up by external metallic strips after a small but precise time delay. These electrons in turn hit other atoms causing an avalanche of electrons. arranged in three 47 groups of four. for instance. We expect them to be produced in the decay of a number of potential new particles. so tracing its path gives a measure of momentum. Because muons can penetrate several metres of iron without interacting. By registering where along the wire electrons hit (in the diagram. more stable and better understood particles. When muons pass through. To identify muons and measure their momenta. while the CSCs are used in the end caps. cathode strip chambers (CSC) and resistive plate chambers (RPC). When a muon or any charged particle passes through the volume it knocks electrons off the atoms of the gas. and are installed in both the barrel and the end caps. COMPACT MUON SOLENOID by the magnetic field.2. RPCs combine a good spatial resolution with a time resolution of just one nanosecond (one billionth of a second). These follow the electric field ending up at the positively-charged wire. at right angles to the wire direction. with drift tubes and resistive-plate chambers in the barrel region. The electrodes are transparent to the signal (the electrons). we get two position coordinates for each passing particle. • Studying the kinematics of pairs of particles produced by the decay of a parent. to be identified. • Searching for events with large amounts of missing transverse energy. The amount of raw data from each crossing is approximately 1 megabytes. and event rate is reduced by a factor of about thousand down to 50 kHz. which implies the presence of particles that have passed through the detector without leaving a signature. an amount that the experiment cannot hope to store.6 Milestones programmable field-programmable gate arrays (FPGA). Physicists are then able to use the Grid to access and run their analyses on the data. The High Level trigger reduces the event rate by a further factor of about a thousand down to around 100 events per second. and those processes that do are well unto identify features of interest such as high energy jets. including: • Performing precision measurements of Standard Model particles. There are a huge range of analyses performed at CMS. derstood. • The insertion of the vacuum tank.4. The trigger system reduces the rate of interesting events down to a manageable 100 per second. EXPERIMENTS the “High Level” trigger. June 2002 If an event is passed by the Level 1 trigger all the data still buffered in the detector is sent over fibre-optic links to • YE+2 descent into the cavern . All the data from each crossing is held in buffers portant strategy because common Standard Model within the detector while a small amount of key inforparticle decays very rarely contain a large number mation is used to perform a fast. • Looking at jets of particles to study the way the partons (quarks and gluons) in the collided protons have interacted. custom hardware using re. such as the Z boson decaying to a pair of electrons or the Higgs boson decaying to a pair of tau leptons or photons. to determine various properties and mass of the parent. approximate calculation of particles.2. In the Standard Model only neutrinos would traverse the detector without being detected but a wide range of Beyond the Standard Model theories contain new particles that would also result in missing transverse energy. Testing the data read-out electronics for the tracker. All these calculations are done on fast. muons or missing energy. or to search for evidence of new physics that manifests in hadronic final states. which allows both for furthering the knowledge of these particles and also for the collaboration to calibrate the detector and measure the performance of various components. let alone process properly. The lower event rate in the High Level trigger allows time for much more detailed analysis of the event to be done than in the Level 1 trigger. a very large number of collisions is required. • Searching for high particle multiplicity final states To accomplish this. This “Level 1” calculation is completed in around 1 µs. Trigger system To have a good chance of producing a rare particle. Most collision events in the detector are “soft” and do not produce interesting effects. a series of “trigger” stages are em(predicted by many new physics theories) is an imployed. These are then stored on tape for future analysis.48 CHAPTER 2. The presence (or not) of any new particles can then be inferred. Data analysis Data that has passed the triggering stages and been stored on tape is duplicated using the Grid to additional sites around the world for easier access and redundancy. such as a Higgs boson. which is software (mainly written in C++) running on ordinary computer servers. which at the 40 MHz crossing rate would result in 40 terabytes of data a second. 2010. form the collaboration who built and operate the detector. 2013. CERN.ch/news/tracker-detector [4] CMS installs the world’s largest silicon detector.96″E / LHCb (standing for "Large Hadron Collider beauty") is one of seven particle physics detector experiments collecting data at the Large Hadron Collider accelerator at CERN.2.4. Ed. Petrilli. (2008-08-14). 2. Alain. Retrieved 2014-03-14. CERN.first pp collisions at 8 TeV”. (Full design documentation) • Copeland.The experiment has wide physics program covering many important aspects of Heavy Flavor (both beauty and formance” (PDF).270 tonnes. The experiment is located at point 8 on the LHC tunnel close to Ferney-Voltaire. S Chatrchyan et al. Random House. Ammir D. (2006). . September 2008 2.10 6°5′48. References • Della Negra. CERN Courier.1088/17480221/3/08/S08004.5 VELO [2] http://cms. the fact that it detects muons. 2008 [5] Using Russian navy shells . Retrieved 2008-08-26. Journal of Instrumentation 3 (8): S08004..ac. Herve. doi:10.click and drag to look around the experiment under construction (with sound!) (requires QuickTime) • The assembly of the CMS detector.ch/content/cms-collaboration Coordinates: 46°14′27.9 Notes 49 • CMS section from US/LHC Website • http://petermccready.4.cern.web. “Inside the CMS Experiment”. France just over the border from Geneva. [8] “New world record .web. finishes its 100 m descent into the CMS cavern.uk/publications/PDF/CERN-CMS. Retrieved 2014-03-14.3S8004T. an important concept in particle physics.the final flurry”. CERN. pdf 2.1 Physics goals Foa. LHCb is a specialized b-physics experiment. They include: • CMS home page • CMS Outreach • CMS Times • Measuring the branching ratio of the rare B → μ+ μ− decay. 2. “CMS Physics Technical Design Report Volume I: Software and Detector Per.5.cern.[10] “CMS” is also a reference to the center-of-mass system. step by step.4. through a 3D animation • The CMS Collaboration.64″N 46.Lucas Taylor [6] Precise mapping of the magnetic field in the CMS barrel yoke using cosmic rays [7] “First lead-ion collisions in the LHC”.2410111°N 6.7 Etymology The term Compact Muon Solenoid comes from the relatively compact size of the detector. Electroweak and QCD physics.8 See also 2.stfc. Retrieved 2014-03-14. Achille. [10] Aczel. Feb 15.0969333°E [3] http://cms. html Panoramic view . The (small) MoEDAL experiment will share the same cavern. [1] http://www. “The CMS experiment at the CERN LHC”. Sixty Symbols. a component of CMS weighing 1.. 2012 2.4. Such studies can help to explain the Matter-Antimatter asymmetry of the Universe. the spokesperson for the collaboration is Guy Wilkinson. Six key measurements have been identified involving B mesons. that is measuring the parameters of CP violation in the interactions of b-hadrons (heavy particles containing a bottom quark). Brady Haran for the University of Nottingham. The detector is also able to perform measurements of production cross sections and electroweak physics in the forward region. These are described in a roadmap document [2] that form the core 2.[1] As of 2014. [9] “LHC report: Run 1 .4.5. VELO • YE+1. Lorenzo. Michel. and the use of solenoids in the detector. Approximately 840 people from 60 scientific institutes. January 2007 • Computer-generated event display of protons hitting a tungsten block just upstream of CMS on the first beam day. CERN.com/portfolio/07041601. Bibcode:2008JInst. charm). 2012. representing 16 countries. “Present at the Creation: Discovering the Higgs Boson”.11 External links physics programme for the first high energy LHC running in 2010–2012. 5. • Measuring properties of radiative B decays. This phase is one of the CP observables with the smallest theoretical uncertainty in the Standard Model. The LHCb detector is a single The main tracking system is placed before and after the arm forward spectrometer with a polar angular coverage dipole magnet. The asymmetry between tracker consists of three subdetectors: the horizontal and vertical plane is determined by a large dipole magnet with the main field component in the ver• The Tracker Turicensis. This implies an enormous flux of particles. The VELO has been designed to withstand integrated fluences of more than 1014 p/cm2 per year for a period of about three years. cated before the LHCb dipole magnet . The detector operates in vacuum and is cooled to approximately −25 °C (−13 °F) using a biphase CO2 system. It is used to reconstruct the trajectories from 10 to 300 milliradians (mrad) in the horizontal and of charged particles and to measure their momenta. The data of the VELO detector are amplified and read out by the Beetle ASIC. • Measuring the CP violating phase in the decay B → J/ψ φ. Specifically.2 The LHCb detector The detector operates at 7 millimetres (0. and can be significantly modified by new Physics. 2. • Charmless charged two-body B decays.e.particle identification of low-momentum tracks. i.50 CHAPTER 2. EXPERIMENTS • Measuring the forward-backward asymmetry of the muon pair in the flavour changing neutral current B → K* μ+ μ− decay. Such a flavour changing neutral current cannot occur at tree-level in the Standard Model of Particle Physics.[3][4] It is used to measure the particle trajectories close to the interaction point in order to precisely separate primary and secondary vertices. Subsystems The vertex detector (VELO) is built around the proton interaction region. caused by interference between the decays with and without B oscillations. It is used for The fact that the two b-hadrons are predominantly pro.28 in) from the LHC beam. • Tree-level determination of the unitarity triangle angle γ. a silicon strip detector lotical direction. these are again flavour changing neutral current decays. The RICH-1 detector (Ring imaging Cherenkov detector) is located directly after the vertex detector. B meson decays with photons in the final states. duced in the same forward cone is exploited in the layout of the LHCb detector. properties of the decay can be strongly modified by new Physics. The 250 mrad in the vertical plane. and only occurs through box and loop Feynman diagrams. 2. Collaboration webpage [2] . The other six are: ATLAS.5.1088/17480221/3/08/S08005.6. Arxiv: First evidence for the decay Bs → μ+ μ[8] “ArXiv Search”. VELO Public Pages 2.6. et al.[9] the LHC 2. Because of this large distance. (LHCb Collaboration) (2008).5.2. Bibcode:2008JInst. CMS. (Full design documentation) 2.5.5 References [1] . photons. The results will complement other high-energy cosmic ray measurements from the Pierre Auger Observatory in Argentina. doi:10. The electromagnetic and hadronic calorimeters provide measurements of the energy of electrons. the smallest of the seven experiments on D0 .4 See also • CERN: European Organization for Nuclear Research • Large Hadron Collider • B-factory 2. LHCF 51 • The Outer Tracker. These measurements are used at trigger level to identify the particles with large transverse momentum (high-Pt particles).[6] These datasets allow them to carry out the physics program of precision Standard Model tests with many additional measurements.6 LHCf The muon system is used to identify and trigger on muons in the events. and LHCb. In 2012 about 2 fb−1 was collected at 8 TeV. and hadrons.. [9] “LHCb experiment observes two new baryon particles never seen before”.. and the Telescope Array Project in Utah. Journal of Instrumentation 3 (8): S08005. those almost directly in line with the colliding proton beams. 19 Nov 2014. Kaons. It therefore consists of two detectors. The LHCf is intended to measure the energy and numbers of neutral pions (π0) produced by the collider.6 External links cated after the dipole magnet covering the outer part of the detector acceptance • LHCb Public Webpage • The Inner Tracker. This will hopefully help explain the origin of ultra-high-energy cosmic rays.5. Roadmap for selected key measurements of LHCb The LHCf ("Large Hadron Collider forward") is a special-purpose Large Hadron Collider experiment for astroparticle (cosmic ray) physics. “The LHCb Detector at the LHC”.[8] New Xi baryons were observed in 2014. The analysis led to evidence for the flavour changing neutral current decay B → μ μ.1 Purpose [5] . 2012 LHC Luminosity Plots [7] . TOTEM. It allows the identification of the particle type of high-momentum tracks. MoEDAL. The LHCb VELO (from the VELO group) [4] .[7] This measurement impacts the parameter space of supersymmetry. • LHCb section from US/LHC Website • A.3S8005T. [3] . Augusto Alves Jr. it can co-exist with a more conventional detector surrounding the interaction point. silicon strip based detector located after the dipole magnet covering the inner part of the detector acceptance Following the tracking system is RICH-2. and The LHCf experiment. LHCf is designed to study the particles generated in the "forward" region of collisions. A straw-tube based detector lo. and shares the interaction point IP1 with the much larger general-purpose ATLAS experiment.2. 2011 LHC Luminosity Plots [6] . ALICE. CP violation was studied in various particle systems such as B . and one of seven detectors in the LHC accelerator at CERN.3 Results During the 2011 proton-proton run LHCb recorded a luminosity of 1 fb−1 [5] at energy 7 TeV. . 140 m on either side of the interaction point. ALICE. search doi:10. The detector aims at measurement of total cross section.52 CHAPTER 2. It shares intersection point IP5 with the Compact Muon Solenoid. LHCf.1 See also • List of Large Hadron Collider experiments 2. Bibcode:2008JInst. doi:10.2 See also 2.6.30972°N longitudinal momentum. Retrieved 2010-03-31. (Full design documentation) • Large Hadron Collider Coordinates: 6. Nov 1. elastic scattering. The other six are: ATLAS. it is possible to obtain infor. Bibcode:2008JInst. These measurements would be unique at the LHC.3S8006T. By detecting protons that have lost less than 1% of their Coordinates: 46°18′35″N 6°04′35″E / 46..6.3S8007T.[1] The aim was to assess the feasibility of installing proton tagging detectors at 420 m from the interaction points of the ATLAS and CMS ex. (TOTEM Collaboration) (2008). (LHCf Collaboration) (2013). • Technical Design Report of LHCf • O Adriani et al. Journal of Instrumentation 3 (8): S08006.3 References • LHCf section on US/LHC Website 2. 2006.23583°N 2. Wonders of the Solar System in 2010 and Wonders of the Universe in 2011.7. International 2.3 External links periments at the Large Hadron Collider (LHC). (Full design documentation) TOTal Elastic and diffractive cross section Measurement (TOTEM) is one of the seven detector experiments at the Large Hadron Collider at CERN. • O Adriani et al.1142/S0217751X13300366.6.7.7 FP420 experiment 2.8. “LHCf detector performance during the 2009-2010 LHC run”..8 TOTEM • The LHCf experiment at LHC For other uses. Bibcode:2013IJMPA. 2.8. CMS.8.07639°E mation that could yield insight on various phenomena of high-energy physics.3 External links • FP420 R&D Project website • Papers and Reviews • LHCf: a tiny new experiment joins the LHC. retrieved on 2009-03-25. see Totem (disambiguation).05500°E 46°14′09″N 6°03′18″E / 46.1 See also Journal of Modern Physics A 28 (25): • CERN: European Organization for Nuclear Re1330036-1. and would be difficult to obtain at both existing and future linear colliders. “The LHCf detector at the CERN Large Hadron Collider”. One notable member of the team was Brian Cox. “The TOTEM Experiment at the CERN Large Hadron Collider”. doi:10.1088/1748-0221/3/08/S08007. EXPERIMENTS 2.7. and diffractive processes. Anelli et al. (LHCf Collaboration) (2008). (Full design documentation) The FP420 R&D project or the FP420 experiment was an international collaboration with members from 29 institutes from 10 countries..2830036A.) 2. LHCb.1088/17480221/3/08/S08006.2.2 References [1] “FP420 R&D Project”. and MoEDAL. (Describes the location of the experiment. who has been • TOTEM Public Webpage involved with BBC in the production of television science • TOTEM section on US/LHC Website documentaries including Horizon. CERN Courier.2 Further reading • G. Journal of Instrumentation 3 (8): S08007. ... 1 Background tency of a maximum of 160 sampling intervals and an integrated derandomising buffer of 16 stages. The pulse shape can 14 be chosen such that it complies with LHCb specifications: By 2012. and LHC voltage after 25 ns of less than 30%.2. It was designed by CERN to handle the prodigious volume of data produced by Large Hadron Collider The chip integrates 128 channels with low-noise charge. oped for the LHCb experiment at CERN.1 Overview 2012. form a dead-timeless readout within 900 ns per trigger. 3.bosons might not be seen in lower energy experiments.[2][3] sensitive pre-amplifiers and shapers.[4][5][6] Either the shaper or comparator output is sampled with the LHC bunch-crossing frequency of 40 MHz into an analog pipeline. Four adjacent comparator channels are being ORed Grid had become the world’s largest computing grid comprising over 170 computing facilities in a worldwide netand brought off chip via LVDS drivers. work across 36 countries. Current drivers bring sought by particle physicists for over 40 years. and because vast numbers of collisions would need to 53 . As of 2012. forThe Beetle ASIC is an analog readout chip. because Higgs The chip can accept trigger rates up to 1. The chip is radiation hardened to an accumulated dose of more than 100 Mrad. A very the serialised data off chip. This ring buffer has a programmable la. Robustness against single event upset is achieved by redundant logic.1.3.Chapter 3 Technology 3.2 LHC Computing Grid Beetle chip The Worldwide LHC Computing Grid (WLCG). data from over 300 trillion (3×10 ) LHC [4] a peaking time of 25 ns with a remainder of the peak proton-proton collisions had been analyzed.1. It is devel. The bias settings and various other parameters can be controlled via a standard I²C-interface.1 MHz to per. A binary readout mode operates at up to important but elusive piece of knowledge that had been 80 MHz output rate on two ports. A comparator per collision data was being produced at approximately 25 channel with configurable polarity provides a binary sig. For analogue The Large Hadron Collider at CERN was designed to readout data is multiplexed with up to 40 MHz onto one prove or disprove the existence of the Higgs boson.merly (until 2006)[1] the LHC Computing Grid (LCG). an or four ports. is an international collaborative project that consists of a grid-based computer network infrastructure incorporating over 170 computing centers in 36 countries.(LHC) experiments.petabytes per year. a charge injector with adjustable pulse height is implemented.a readout chip for LHCb • The Large Hadron Collider beauty experiment 3.1 Beetle (ASIC) For testability and calibration purposes. The LHC Computing nal. powerful particle accelerator was needed. as of 3.2 External links • Beetle . com. distribute and analyse the ~25 Petabytes (25 million Gigabytes) of data annually generated by the Large Hadron Collider” [6] What is the Worldwide LHC Computing Grid? (Public 'About' page) 14 November 2012: “Currently WLCG is made up of more than 170 computing centers in 36 countries. Therefore advanced computing facilities were needed to process the data. “Parallel Internet: Inside the Worldwide LHC computing grid”. [13] final-draft-4-key [14] Brodkin. The Times (London). The Tier 1 institutions receive specific subsets of the raw data. Techworld. via dedicated 10 Gbit/s links. This data is sent out from CERN to eleven Tier 1 academic institutions in Europe. CERN. [8] “LHC GridFest”. [9] Jonathan Leake (6 April 2008). The CERN computer center.[9] CERN had to publish its own articles trying to clear up the confusion. which represents the output of calculations done by the CPU farm at the CERN data center..[11] [4] Hunt for Higgs boson hits key decision point [5] Worldwide LHC Computing Grid main page 14 November 2012: "[A] global collaboration of more than 170 computing centres in 36 countries . Retrieved 2 October 2011. Re..2. “Coming soon: superfast internet”. to store. 3. CERN.[11] The data stream from the detectors provides approximately 300 GByte/s of data.[13] The data produced by the LHC on all of its distributed computing grid is expected to add up to 10–15 PB of data each year.5 External links tion is necessary. Adapted from an article originally published in Symmetry Breaking. has a dedicated 10 Gbit/s connection to the counting room. 20 June 2005. Retrieved 25 January 2013. • “Official website”. Retrieved 2 October 2011. the four main detectors at the LHC produced 13 petabytes of data in 2010.[13] The primary configuration for the computers used in the grid is based on Scientific Linux. [2] What is the Worldwide LHC Computing Grid?.2. This is called the LHC Optical Private Network. 2008.2. Retrieved 25 January 2013. CERN. Distributed computing resources for analysis by enduser physicists are provided by the Open Science Grid.[12] More than 150 Tier 2 institutions are connected to the Tier 1 institutions by general-purpose national research and education networks. TECHNOLOGY be studied. ISBN 92-9083-253-3. and LHC@home .1038/469282a. Educational web site. “Happy 10th Birth. Jacqui (21 December 2011). LHC@home consists of two applications: LHC@home Classic.000 processing cores and 150 petabytes of disk space. Enabling Grids for E-sciencE.[8] A popular 2008 press article predicted “the internet could soon be made obsolete” by its technology. Retrieved 2012-12-20. retrieved 2012-01-11 [3] Welcome. Such a collider would also produce unprecedented quantities of collision data requiring analysis. January 2011. trieved 2012-12-20. 3. Asia.3 LHC@home LHC@home is a distributed computing project for particle physics based on the Berkeley Open Infrastructure for Network Computing (BOINC) platform. [11] Geoff Brumfiel (19 January 2011). for which they serve as a backup repository for CERN. “High-energy physics: Down the petabyte highway”.. CERN.[14] In total. CERN-LHCC-2005-024 (The LCG TDR Editorial Board). [12] “Network transfer architecture”. WLCG!".2.54 CHAPTER 3. Jon (28 April 2008). results in a data stream of about 300 MByte/s. Nature 469: 282–283.[13] and LHC@home projects.[10] It incorporates both private fiber optic cable links and existing high-speed portions of the public Internet. Retrieved 2 October 2011. International Grid Science This Week.3 See also • Openlab (CERN) • “GridCafé". SixTrack. doi:10. January 2011. May 2008. CERN. and North America.. the Grid consisted of some 200. They also perform reprocessing when recalibra.4 References and is used to upgrade and maintain the particle acceler[1] Hayes. retrieved 2012-01-11 3. which went live in September 2004 3.[7] It was announced to be ready for data on 3 October 2008.nization for Nuclear Research (CERN). At the end of 2010.2 Description A design report was published in 2005. which after filtering for “interesting events”.The WLCG is now the world’s largest computing grid” [7] LHC Computing Grid: Technical Design Report.ator Large Hadron Collider (LHC) of the European Orgaday. document LCG-TDR-001. distributed across 34 countries. CERN. considered “Tier 0” of the LHC Computing Grid. plus 10 TB of “event summary data”. The project was expected to generate 27 TB of raw data per day.3. [10] “The Grid: separating fact from fiction”. Test4Theory uses VirtualBox.3. is the first and smallest circular proton accelerator in the accelerator chain at the CERN Large Hadron Collider injec• A new experimental version called SixTrackbnl tion complex . a synchrotron. SixTrack simulates particles accelerating through the 27 km (17 mi)-long LHC to find their orbit stability. and to predict possible problems that could arise from adjustment or modification of the LHC’s equipment. Data from the project is utilized by engineers to improve the operation and efficiency of the accelerator. overview”.4. This is sixtrack. The ring-shaped 10 seconds in an actual run.com.4.3. and receives no funding from CERN. 3. contains four superimposed rings with a radius of 25 meters. which would take about The surface above the PS Booster at CERN. which are sent to a central project server upon completion. on September 29 to commemorate CERN’s 50th anniversary.[1][2] LHC@home uses idle computer process2011.4 workunits have been seen lately. • The orbit stability data is used to detect if a particle in orbit goes off-course and runs into the tube wall—if this happened too often in actual running. GeV. boincstats. and runs on a variety of hardware configurations. It takes protons with an energy of 50 MeV from the • Garfield is a newer application.2 See also • Citizen Cyberscience Centre • LHC Computing Grid • List of distributed computing projects 3.3.4 External links platform.Credit vide a reference to test the measurements performed at [1] Willy de Zutter. which went live in August 2011 and is 3. downloaded via BOINC onto participant computers running Windows.1 See also 3. • LHC@home Classic Project Page 3. • SixTrack homepage • Test4Theory Project Page 3. “LHC Test4Theory@Home . Linux or Mac OS X. • In one workunit.2 External links • PS Booster Machine: layout and photographs .000. There are currently no plans to use the project to do computation on the data that will be collected by the LHC.3.4 Proton Synchrotron Booster The project software involves a program called SixTrack. The project went public.000 loops. The Proton Synchrotron Booster.Credit combined more than 15. The accelerator was built in 1972. ready to be injected into the Proton Synchrotron.3. The applications are run with the help of about fifteen thousand active volunteered computers processing at a [2] Willy de Zutter. boincstats.4.0.1 SixTrack The project was first introduced as a beta on 1 September 2004 and a record 1000 users signed up within 24 hours. with a 5000 user limit. created by Frank Schmidt. and started to be sent to computers in early November.3 References used to simulate high-energy particle collisions to pro“LHC@Home Classic . PROTON SYNCHROTRON BOOSTER 55 2. although not many linear accelerator Linac2 and accelerates them up to 1. accelerator is visible as a circular building that rises from the ground. Test4Theory. this would cause damage to the accelerator which would need repairs. Retrieved 16 December the LHC.000 or 1. The project is cross. Currently there is no user limit and qualification. ing resources from volunteers’ computers to perform calculations on individual workunits. an x86 virtualization • LHC@home Project Page software package. The project is administered by volunteers.com.5 teraFLOPS on average as of overview”. Retrieved 16 December June 2014.3. 2011. 60 particles are simulated travelling 100. and can be The vertex detector (VELO) is built around the proton interaction region. and only occurs through box and loop Feynman diagrams.ences of more than 1014 p/cm2 per year for a period of gle γ. This phase is Subsystems one of the CP observables with the smallest theoretical uncertainty in the Standard Model. caused by interference between the decays with and without B oscillations.2410111°N 6.5. about three years. 6°5′48.5. Approximately 840 people from 60 scientific institutes.[3][4] It is used to measure the particle significantly modified by new Physics. The detector is also able to perform measurements of production cross sections and electroweak physics in the forward region. Such a flavour changing neutral current cannot occur at tree-level in the Standard Model of Particle Physics. form the collaboration who built and operate the detector. the spokesperson for the collaboration is Guy Wilkinson.56 CHAPTER 3. TECHNOLOGY 3. properties of the decay can be strongly modified by new Physics. trajectories close to the interaction point in order to pre• Measuring properties of radiative B decays. tral current decays.5 VELO Coordinates: 46°14′27.The detector operates at 7 millimetres (0.28 in) from the LHC beam.0969333°E • Charmless charged two-body B decays. cisely separate primary and secondary vertices. France just over the border from Geneva.64″N 46. Such studies can help to explain the Matter-Antimatter asymmetry of the Universe. Six key measurements have been identified involving B mesons.1 3. The LHCb detector is a single arm forward spectrometer with a polar angular coverage from 10 to 300 milliradians (mrad) in the horizontal and 250 mrad in the vertical plane. They include: • Measuring the branching ratio of the rare B → μ+ μ− decay. representing 16 countries. i. The VELO has been designed to withstand integrated flu• Tree-level determination of the unitarity triangle an. The detector operates in vacuum and is . that is measuring the parameters of CP violation in the interactions of b-hadrons (heavy particles containing a bottom quark). • Measuring the CP violating phase in the decay B → J/ψ φ. LHCb is a specialized b-physics experiment.2 The LHCb detector The fact that the two b-hadrons are predominantly produced in the same forward cone is exploited in the layout of the LHCb detector.96″E / LHCb (standing for "Large Hadron Collider beauty") is one of seven particle physics detector experiments collecting data at the Large Hadron Collider accelerator at CERN. these are again flavour changing neu. Physics goals The experiment has wide physics program covering many important aspects of Heavy Flavor (both beauty and charm).[1] As of 2014. These are described in a roadmap document [2] that form the core physics programme for the first high energy LHC running in 2010–2012. • Measuring the forward-backward asymmetry of the muon pair in the flavour changing neutral current B → K* μ+ μ− decay. The (small) MoEDAL experiment will share the same cavern. The experiment is located at point 8 on the LHC tunnel close to Ferney-Voltaire. Electroweak and QCD physics.e. This implies an enormous flux of particles. 3. B meson decays with photons in the final states. The asymmetry between the horizontal and vertical plane is determined by a large dipole magnet with the main field component in the vertical direction. Specifically. The analysis led to evidence for the flavour changing neutral current decay B → μ μ. and hadrons..6 External links • LHCb Public Webpage • LHCb section from US/LHC Website • A.3S8005T. It is used to reconstruct the trajectories of charged particles and to measure their momenta. A straw-tube based detector located after the dipole magnet covering the outer part of the detector acceptance • The Inner Tracker. The RICH-1 detector (Ring imaging Cherenkov detector) is located directly after the vertex detector. It is used for particle identification of low-momentum tracks. The electromagnetic and hadronic calorimeters provide measurements of the energy of electrons. In 2012 about 2 fb−1 was collected at 8 TeV. 3. (LHCb Collaboration) (2008). a silicon strip detector located before the LHCb dipole magnet • The Outer Tracker. 3.5. photons.[8] New Xi baryons were observed in 2014. doi:10. Bibcode:2008JInst. silicon strip based detector located after the dipole magnet covering the inner part of the detector acceptance Following the tracking system is RICH-2. The LHCb VELO (from the VELO group) [5] . 19 Nov 2014. The data of the VELO detector are ampli[1] . The tracker consists of three subdetectors: [4] . CP violation was studied in various particle systems such as B . Journal of Instrumentation 3 (8): S08005. et al. 2012 LHC Luminosity Plots [7] . 2011 LHC Luminosity Plots [6] . It allows the identification of the particle type of high-momentum tracks. VELO 57 cooled to approximately −25 °C (−13 °F) using a biphase 3. These measurements are used at trigger level to identify the particles with large transverse momentum (high-Pt particles). Collaboration webpage fied and read out by the Beetle ASIC.3.5.[9] 3.. and D0 .[7] This measurement impacts the parameter space of supersymmetry.5. “The LHCb Detector at the LHC”. (Full design documentation) . VELO Public Pages [3] . The muon system is used to identify and trigger on muons in the events. [9] “LHCb experiment observes two new baryon particles never seen before”.[6] These datasets allow them to carry out the physics program of precision Standard Model tests with many additional measurements. Kaons.5 References CO2 system.3 Results During the 2011 proton-proton run LHCb recorded a luminosity of 1 fb−1 [5] at energy 7 TeV. Augusto Alves Jr.4 See also • CERN: European Organization for Nuclear Research • Large Hadron Collider • B-factory [8] “ArXiv Search”.5. Arxiv: First evidence for the decay Bs → μ+ μ- • The Tracker Turicensis. Roadmap for selected key measurements of LHCb The main tracking system is placed before and after the dipole magnet. [2] .5.1088/17480221/3/08/S08005. The development of the Standard Model was driven by cles known. and strong nuclear in. as a collaborative effort of scientists theorists. and the gauge bosons). the Standard Model is a paradigm of a quantum around the world.lations (and their non-zero masses). It was developed throughout the latter half theoretical and experimental particle physicists alike. extra dimensions. with the three generations of matter. For of the 20th century. masses. weak and electromagnetic forces. chiralities. This article is a non-mathematical general overview of the Standard Model. The model does not symmetry breaking. as well as classifying all the subatomic parti. Although the Standard Model is believed to be theoretically self-consistent[2] and has demonstrated huge and continued successes in providing experimental predicStandard Model of Particle Physics.of gravitation[3] as described by general relativity. Because of its success in explain. and in. teractions. it does leave some phenomena unexplained and elementary particles of the Standard Model (the Higgs boson. cosmology. and the Higgs boson in the fifth. It is used as a basis for buildquark (1995). tal interactions.field theory. see Standard model (disambiguation). anomalies. the tau neutrino (2000). erything”. the Standard results at variance with the Standard Model. The diagram shows the tions. For other uses. nonthe existence of quarks. It also does not incorporate neutrino oscilcerning the electromagnetic. etc. or acteractions with the strong.1 Standard Model This article is about the Standard Model of particle physics.[1] The current formulation was final. which exhibits a wide range of physics inized in the mid-1970s upon experimental confirmation of cluding spontaneous symmetry breaking. Since then. and elaborate symmetries (such the Standard Model.as supersymmetry) in an attempt to explain experimental ing a wide variety of experimental results. charges. The Standard Model of particle physics is a theory con- The Standard Model of elementary particles (more schematic depiction). weak. and shows how the properties of the various contain any viable dark matter particle that possesses all particles differ in the (high-energy) symmetric phase (top) and of the required properties deduced from observational the (low-energy) broken-symmetry phase (bottom). It count for the accelerating expansion of the universe (as also depicts the crucial role of the Higgs boson in electroweak possibly described by dark energy). For a mathematical description. the it falls short of being a complete theory of fundamenthree generations of quarks and leptons.Chapter 4 Theory 4. see the article Standard Model (mathematical formulation).existence of dark matter and neutrino oscillations. It does not incorporate the full theory including their names. have given further credence to ticles. spins. such as the Model is sometimes regarded as a “theory of almost ev. discoveries of the top perturbative behavior. and more recently ing more exotic models that incorporate hypothetical parthe Higgs boson (2013). gauge bosons in the fourth column. 58 . STANDARD MODEL 4. electron neutrino. charges they carry). physics has reduced the laws govern. of which all the other ing color-neutral composite particles (hadrons) containknown laws would be special cases. which makes them notoriously difficult to detect. such as color charge.1. and their masses The pattern of weak isospin. A phenomenon called color confinement results in mon ground” that would unite all of these theories into quarks being very strongly bound to one another. matter and energy are best understood in trino). which in turn can be distinguished by other characteristics. There are six quarks (up. Fermions The remaining six fermions do not carry colour charge and are called leptons. the quarks and leptons. Each fermion has a corresponding antiparticle. and tau all interact electromagnetically.[10][11][12][13] the electroweak theory became widely accepted and Glashow. Hence they interact with other fermions both electromagnetically and 4. Seccording to how they interact (or equivalently. and the Higgs boson). fermions respect the Pauli exclusion principle. the electron.clei ultimately constituted of up and down quarks.e. strange. muon. Q eL YW uR θW dL H νR g dL ϕ+ eR W+ uL dR g8 3 γ g Z T3 H* νL 0 dR uR uL After the neutral weak currents caused by Z boson exϕeR WeL change were discovered at CERN in 1973. The first generation charged particles do not decay. posed of fractionally charged quarks.[4] In 1967 Steven Weinberg[5] and Abdus Salam[6] incorporated the Higgs mechanism[7][8][9] into Glashow’s electroweak theory. interact via the strong interactheories. The familiar proton and the neutron [14] least in principle).1. rotated by the were found to be as the Standard Model predicted. with corresponding particles exparticles. and from which the ing either a quark and an antiquark (mesons) or three behavior of all matter and energy could be derived (at quarks (baryons). to which many the vertical. YW.hibiting similar physical behavior (see table). However.4. formone integrated theory of everything. and color charge of all known elementary particles. tau.1 59 Historical background The first step towards the Standard Model was Sheldon Glashow's discovery in 1961 of a way to combine the electromagnetic and weak interactions. i. charm. ing the behavior and interaction of all known forms of The defining property of the quarks is that they carry matter and energy to a small set of fundamental laws and color charge. weak hypercharge. all atoms consist of electrons orbiting atomic nuThe fermions of the Standard Model are classified ac. on the other The Standard Model includes 12 elementary particles of spin-½ known as fermions. T3 . by virtue of carrying an electric charge. Each member of a generation has greater mass than the corresponding particles of lower generations. roughly along The theory of the strong interaction.1. According to the spinstatistics theorem. are the two baryons having the smallest mass. 4. tau neuAt present. electroweak symmetry and interacts with other particles to give when experiments confirmed that the hadrons were com. The W and Z bosons were discovered experimentally in 1981. weak mixing angle to show electric charge. The Higgs mechanism is believed to give rise to the masses of all the elementary particles in the Standard Model. and hence. Q. giving it its modern form. A major goal of physics is to find the “comtion. The three neutrinos do not carry electric charge either. top. Salam. To date. and Weinberg shared the 1979 Nobel Prize in Physics for discovering it.3 Particle content via the weak interaction. Quarks also carry electric charge and weak isospin. and the masses of the fermions. bottom). gauge bosons. hence all ordinary (baryonic) matter is made of such particles.them mass. by what ond and third generations charged particles. down. Specifically. Pairs from each classification are grouped together terms of the kinematics and interactions of elementary to form a generation.2 Overview The Standard Model includes members of several classes of elementary particles (fermions. muon neutrino. muon. and six leptons (electron. so their motion is directly influenced only by the weak nuclear force. acquired its modern form around 1973–74. This includes the masses of the W and Z bosons.1. The neutral Higgs field (gray square) breaks the contributed. . Feynman diagrams in the standard model are built from these vertices. weak. red–antigreen). The electrically neutral Z boson interacts with both left-handed particles and antiparticles. They are massive. The photon is massless and is well-described by the theory of quantum electrodynamics. The different types of gauge bosons are described below. These three gauge bosons along with the photons are grouped together. as collectively mediating the electroweak interaction.g. The gauge bosons of the Standard Model all have spin (as do matter particles). As a result. The Feynman diagram calculations. Gluons are massless. the conjugate of each listed vertex (i. Modifications involving Higgs boson interactions and neutrino oscillations are omitted. The weak interactions involving the W± exclusively act on left-handed particles and right-handed antiparticles. and Z gauge bosons mediate the weak interactions between particles of different flavors (all quarks and leptons). At a macroscopic level. The above interactions form the basis of the standard model. CHAPTER 4. and electromagnetic fundamental interactions. These include low-energy quantum chromodynamics. reversing the direction of arrows) is also allowed. • Photons mediate the electromagnetic force between electrically charged particles. W−. and gravitation allows particles with mass to attract one another in accordance with Einstein’s theory of general relativity.g. making them bosons. and solitons.e. and the particle is therefore said to have mediated (i. perturbation theory (and with it the concept of a “force-mediating particle”) fails in other situations. with the Z being more massive than the W±.[nb 1] Because the gluons have an effective color charge. However. • The eight gluons mediate the strong interactions between color charged particles (the quarks).. and when applied to analyze high-energy scattering experiments are in reasonable agreement with the data. decay with very short half lives. bound states. Furthermore. When a force-mediating particle is exchanged. .e. which are a graphical representation of the perturbation theory approximation. Neutrinos of all generations also do not decay. but rarely interact with baryonic matter.60 hand. at a macroscopic level the effect is equivalent to a force influencing both of them. been the agent of) that force. electromagnetism allows particles to interact with one another via electric and magnetic fields. The Standard Model explains such forces as resulting from matter particles exchanging other particles. photons) do not have a theoretical limit on their spatial density (number per volume). The charge of the W bosons is dictated by the fermions they interact with. generally referred to as force mediating particles. THEORY Interactions in physics are the ways that particles influence other particles. the W± carries an electric charge of +1 and −1 and couples to the electromagnetic interaction. The value of the spin is 1. invoke “force mediating particles”. and are observed only in very high-energy environments. gauge bosons are defined as force carriers that mediate the strong. Gauge bosons Summary of interactions between particles described by the Standard Model. they do not follow the Pauli exclusion principle that constrains fermions: thus bosons (e. In the Standard Model. • The W+. The gluons and their interactions are described by the theory of quantum chromodynamics. they can also interact among themselves. and pervade the universe. The eightfold multiplicity of gluons is labeled by a combination of color and anticolor charge (e. 4. El. it must interact with itself. As the Higgs boson is inertial reference frame invariance central to the theory massive. The fields fall into different representations of the Higgs boson using the Large Hadron Collider (LHC) the various symmetry groups of the Standard Model (see at CERN began in early 2010. they are not affected by this sector. the LHC (designed to collide two 7 to strength λ ~ 1/8). and for that reason is classified as a boson matical framework for the Standard Model. are critical metries. and Tom Kibble in 1964 Construction of the Standard Model Lagrangian (see 1964 PRL symmetry breaking papers) and is a key building block in the Standard Model.[19][20][21][22][23] On 14 March 2013 the Higgs Boson was tentatively confirmed to exist. Each kind of particle is described in terms of a Model. Experiments to confirm and determine the nature of actions. the three factors of the high-energy particle accelerator can observe and record gauge symmetry give rise to the three fundamental interit. are massive. which is “consistent with the Higgs boson.[24] LQCD = iU (∂µ −igs Gaµ T a )γ µ U +iD(∂µ −igs Gaµ T a )γ µ D. whose ematical consistency of the Standard Model requires that numerical values are established by experiment. the tivistic quantum field theories.” Although interactions between quarks a metry. and among the many color states of quarks and gluons. and exactly which version of the Standard Model Higgs is best supported if confirmed. It consists of the familHiggs boson generates the masses of the leptons (eleciar translational symmetry. of special relativity. The local SU(3)×SU(2)×U(1) gauge Because the Higgs boson is a very massive particle and symmetry is an internal symmetry that essentially defines also decays almost immediately when created. Roughly. one Fermilab's Tevatron until its closure in late 2011. STANDARD MODEL 61 The interactions between all the particles described by the Full particle count Standard Model are summarized by the diagrams on the Counting particles by a rule that distinguishes beright of this section. on the order of 10−25 The quantum chromodynamics (QCD) sector defines the and gluons. Math.postulating a set of symmetries of the system. Lagrangian controls the dynamics and kinematics of the The Higgs boson plays a unique role in the Standard theory. François Englert. Since leptons do not interact with it has several properties similar to the predicted “simgluons. with SU(3) symkg). The paany mechanism capable of generating the masses of el. The Dirac La[18] they acknowledged that further work plest” Higgs. to many aspects of the structure of microscopic (and The global Poincaré symmetry is postulated for all relahence macroscopic) matter. and then by ementary particle masses.4 Theoretical aspects Main article: Standard Model (mathematical formulation) The Higgs particle is a massive scalar elementary particle theorized by Robert Brout.finds that the dynamics depend on 19 parameters.tion of the Standard Model proceeds following the modticular. Upon writing the most general Lagrangian. C. which have integer spin). muon. and the differences between writing down the most general renormalizable Lagrangian electromagnetism (mediated by the photon) and the weak from its particle (field) content that observes these symforce (mediated by the W and Z bosons). The construccles. the Higgs self-coupling TeV. the Higgs boson explains why the photon has no ern method of constructing most field theories: by first mass. while the W and Z bosons are very heavy. gives a total of 61 elementary particles. only a very the Standard Model. in which a (like the gauge bosons. by explaining why the other elementary parti. grangian of the quarks coupled to the gluon fields is given would be needed to conclude that it is indeed the Higgs by boson. In electroweak theory. R. .[25] Higgs boson Main article: Higgs boson 4. Hagen. In par.4 the Higgs mass is at 125 GeV. the two main experiments at the LHC Quantum chromodynamics (ATLAS and CMS) both reported independently that they found a new particle with a mass of about 125 GeV/c2 (about 133 proton masses. except the photon and gluon. rotational symmetry and the tron.1.[17] Quantum chromodynamics sector Main article: On 4 July 2012.1.rameters are summarized in the table above (note: with ementary particles become visible at energies above 1. and were performed at table). 8 TeV proton beams) was built to answer the question of whether the Higgs boson actually exists. and tau) and quarks. Gerald Guralnik.[16] therefore.[7][8][9][15] It has no Technically. quantum field theory provides the matheintrinsic spin.dynamical field that pervades space-time. Peter Higgs. tween particles and their corresponding antiparticles. generated by T . found the change (∆μ/μ) in the proton-to-electron ( + ) 1 φ mass ratio μ to be equal to "(0. 2 2 4 path-integrals) has not been mathematically proven. studying methanol molecules in a distant galaxy. the results are a potential sign of something amiss and are likely to impact existing theories. Higgs sector Main article: Higgs mechanism In May 2012 BaBar Collaboration reported that their recently analyzed data may suggest possible flaws in the Standard Model of particle physics. While regularized versions useful for approximate comwhich can also be written as: putations (for example lattice gauge theory) exist. Before symmetry breaking. 2012. physicists reported the conIn the Standard Model. Their predicted properties were experimentally confirmed with good preElectroweak sector Main article: Electroweak inter. it is not known whether they converge (in the sense of S-matrix elements) in the limit that the regulator is removed.cision. and the top and charm quarks before these particles were observed.[30] On December 13.1. and g is the strong The Standard Model (SM) predicted the existence of the coupling constant. In this type of decay. W and Z bosons. gluon. a particle called the B-bar meson decays into a D meson.0 ± 1. W three-component SU(2) gauge field. While the level of certainty of the excess (3.62 CHAPTER 4. the Higgs Lagrangian is: Challenges See also: Physics beyond the Standard Model Self-consistency of the Standard Model (currently formu( )) ( )) i( ′ i ( ′ lated as a non-abelian λ2 ( † theory2 )quantized 2 through ⃗µ ⃗µ LH = φ† ∂ µ − g YW B µ + g⃗τ W ∂µ + g YW Bµ + g⃗τ W φ − gauge φ φ−v . over space and time. The weak isospin (YW) of both com. including those attempting to deduce the properties of Higgs bosons. of Z bosons. To give an idea of the success of the SM.4 sigma) is not enough to claim a break from the Standard Model. which have been experimentally confirmed by the Large Electron-Positron Collider at CERN. LEW = ∑ ψ ( ) ¯ µ i∂µ − g ′ 1 YW Bµ − g 1 ⃗τL W ⃗µ ψ ψγ 2 2 where Bμ is the U(1) gauge field.[31][32] where the indices + and 0 indicate the electric charge (Q) of the components.4. The scientists. g′ and g are coupling constants.1.and down-type quarks.0) × 10−7 at redshift φ= √ .89” and consistent with “a null result". φ0 2 z = 0. an antineutrino and a tau-lepton. of a basic physical constant of the group SU(2)L: of nature that supports the standard model of physics. the Higgs field is a complex scalar stancy. A .7 ponents is 1. γ µ are 4. D and U are the Dirac spinors associated with up. the folaction lowing table compares the measured masses of the W and Z bosons with the masses predicted by the SM: The electroweak sector is a Yang–Mills gauge theory with The SM also makes several predictions about the decay the simple symmetry group U(1)×SU(2)L.[28][29] These data show that a particular type of particle decay called “B to D-star-tau-nu” happens more often than the Standard Model says it should. The subscript L indicates that they only act on left fermions. THEORY Gaµ is the SU(3) gauge field containing the gluons. YW is the weak hy⃗ µ is the percharge—the generator of the U(1) group.6 Tests and predictions the Dirac matrices. ⃗τL are the Pauli matrices—infinitesimal generators of the SU(2) group. ( . ) ) . . 2 λ2 ( † i( ′ 2 key)question related to the consistency is the Yang–Mills ⃗ . . LH = . ∂µ + g YW Bµ + g⃗τ Wµ φ. Those particles are called force tal level.[26] anism where heavy right-handed neutrinos are added to . this an exchange of bosons between the objects affected. such can be achieved by adding a non-renormalizable interacas a photon for the electromagnetic force and a gluon for tion of leptons with the Higgs boson.[34] On a fundamenthe strong interaction. Experiments indicate that neutrinos have mass.5 Fundamental forces date this finding. the classic Standard Model can be modThe Standard Model classified all four fundamental forces ified to include neutrino mass. − φ φ − v2 . 2 4 existence and mass gap problem. In the Standard Model.[33] To accommo4.1. such an interaction emerges in the seesaw mechcarriers. in nature. a force is described as If one insists on using only Standard Model particles. which the classic Standard Model did not allow. This is natural in the left-right symmetric ex. other scenarios that in4.g. ISBN 978-1-42008298-2.D. Sakurai Prize for Theoretical Particle Physics terms of quantum field theory. Accessed Oct.). strictly speaking. Quark matter. 2. Penguin Group. The isotropy and homogeneity of the visible universe over large distances seems to require a mechanism like cosmic inflation. Quark model extend the Standard Model into a Unified field theory or • Weak interaction: Electroweak theory. The Teaching Company. Guidebook Part 2 page 59. [2] In fact. there are. masses. there is no known way of describing general relativity. however. Landau pole). 2007. CP violation. no proposed Theory of Everything has been widely accepted or verified. • J. ". CRC Press.4. the Standard Model cannot explain the observed amount of cold dark matter (CDM) and gives contributions to dark energy which are many orders of magnitude too large. Quantum triviality • Some consider it to be ad hoc and inelegant.1.Standard Model of Particle Physics: The modern theory of elementary particles and their interactions .g. For a further discussion see e. STANDARD MODEL 63 the theory. • It should be modified so as to be consistent with the emerging “Standard Model of cosmology. • The Higgs mechanism gives rise to the hierarchy [1] Technically. [3] Sean Carroll. Inadequacies of Weak isospin the Standard Model that motivate such research include: • Gauge theory: Nontechnical introduction to gauge theory • It does not attempt to explain gravitation.. J. • Strong interaction: Color charge. Ward the canonical theory of gravitation..” In particular. Higgsless model troweak interactions of the Standard Model.. but the predictions extracted from the Standard Model by current methods applicable to current experiments are all self-consistent. Neutrino masses. the Unsung Triumph of Modern Physics to create a consistent quantum field theory involving (Kindle ed. As a consequence. can explain why neutrinos have • Standard Model: Mathematical formulation of. Although the Standard Model. among other things. An Introduction to Particle Physics and the Standard Model. However. we have no reliable • Open questions: BTeV experiment. Weak hypercharge. p.. which would also constitute an extension of the Standard Model. there is one color-symmetric combinaproblem if some new physics (coupled to the Higgs) tion that can be constructed out of a linear superposition is present at high energy scales. The Theory of Almost Everything: The triviality. It does not. physical phenomena including constants. 2013. Cal Tech.[37] As long as new physics appears below 14 or around 10 GeV. reducing the count to eight. that quantum field theories • Lagrangian of gravity generally break down before reaching the Planck scale. include gravity.10 References clude quantum gravity in which such fine tuning can be avoided. severe fine tuning of the parameters is required. [38] There are also issues of Quantum [1] R. consistently in • J. elementary scalar particles. Chapter 25 of R.. although a theoretical particle known as a graviton would • Generation help explain it. 7. as it now stands.1. although it’s often convenient to include gravitons among the known particles of nature.9 Notes and references also arbitrary parameters. C. Mann (2010). requir• Penguin diagram ing 19 numerical constants whose values are unre• Quantum field theory lated and arbitrary. Dark Matter. Oerter (2006). theory for the very early universe. which suggests that it may not be possible Standard Model. The reason for this is.. a complete theory explaining all theory of beta decay. which are 4. It is believed that explaining neutrino mass will require an additional 7 or 8 constants. the specifics of neutrino mass are still unPhysics beyond the Standard Model clear. In these cases in orof the nine combinations.8 See also tension of the Standard Model [35][36] and in certain grand • Fundamental interaction: unified theories. Quantum Theoretical and experimental research has attempted to chromodynamics. and unlike for the strong and elec• Higgs mechanism: Higgs boson.1.” . Ph.. there are nine such color–anticolor combinations. the neutrino masses can be of the • Quantum electrodynamics right order of magnitude. Dark Energy: The Dark Side of the Universe. Currently.4.1. Fermi a Theory of everything. It is also difficult to accommodate the observed predominance of matter over antimatter (matter/antimatter asymmetry). der for the weak scale to be much smaller than the Planck scale. ISBN 0-13-2366789. there are mathematical issues regarding quantum field theories still under debate (see e. “Partial-symmetries of weak interactions”.585G. Giacomelli. Glashow (1961).13. 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[12] F.. “Weak interactions at very high energies: The role of Physical Review D 16 the Higgs-boson mass”. Guralnik (2009). Retrieved 2012-07-05. [23] D. Physical Review Letters 19 (21): 1264–1266.339. Stockholm: Almquvist and Wiksell..1519L. “Evidence for an excess of B → D(*) τ− ντ decays”.. “Higgs Discovery: Is it a Higgs?".16.. Space. 14 March 2013.... CHAPTER 4. [26] http://home. T. pp.1566..64 [4] S. Retrieved 2013-08-06..24. YouTube. Physical Review Letters 13 (9): 321–323. [16] B. 4 July 2012.321E. 313–314. doi:10.19.101802. [32] C. Nuclear Physics 22 (4): 579–588.jhu. 11 November 2009. [17] “Huge $10 billion collider resumes hunt for 'God particle'".1224898. CERN.. [34] S.43. Bibcode:1973PhLB.138H. doi:10. Bibcode:1961NucPh..1103/PhysRevLett. “Broken Symmetry and the Mass of Gauge Vector Mesons”.579G. doi:10.. which is almost never. Retrieved 2010-05-04.19. 4 July 2012. THEORY (5): 1519–1531. [22] “Confirmed: CERN discovers new particle likely to be the Higgs boson”. Physical Review Letters 13 (20): 585–587.. doi:10. SLAC.46B. Retrieved 2012-07-05. [30] “BaBar data hint at cracks in the Standard Model”. ATLAS. Retrieved 2012-07-04.S.1103/PhysRevLett. doi:10. Bibcode:1967PhRvL. Retrieved 2013-08-06. [33] “Particle chameleon caught in the act of changing”. (2012). (1974). Physical Review Letters 43 (21): 1566.1103/PhysRevLett.J. Quigg...13.1103/PhysRevLett.508. Eighth Nobel Symposium. Physical Review Letters 109 (10): 101802. Thacker (1977). arXiv:1205. “Observation of neutrino-like interactions without muon or electron in the Gargamelle neutrino experiment”. pp. CERN.pha. Salam (1968).J. Kibble (1964). Physics Letters B 46 (1): 138.2601G. . 2–7 [31] J.. Weinberg (1967). Nuclear Physics B 73 (1): 1.1016/03702693(73)90499-1.R. Higgs (1964).edu/~{}dfehling/particle. Bibcode:1974NuPhB.. [9] G. Haidt (4 October 2004). Bibcode:1964PhRvL. “The discovery of the weak neutral currents”.. Hasert et al. Englert. “Basic Constituents of Matter and their Interactions — A Progress Report”. Wilczek (2004).P. Springer. Physical Review Letters 44 (14): 912–915. Senjanovic (1980).. Cambridge University Press. ISBN 3-540-676724.4226. Gauge Theories in Particle Physics: A Practical Introduction. Gauge Theory of Weak Interactions.. "μ → e γ at a Rate of One Out of 109 Muon Decays?". Roy (1999). • B.4.L. Donoghue.1.. • S.001. Johns Hopkins University Press. Quantum Field Theory and the Standard Model (Сambridge University Press 2013) 952 pages • Langacker P. “Search for Proton Decay through p → νK + in a Large Water Cherenkov Detector”.12 External links mentary particle physics.. G. Minkowski (1977).1016/03701573(73)90027-6. Aitchison. • Nagashima Y. van Nieuwenhuizen and D.. North Holland.2716. Gauge theory of ele. The standard model and beyond.2004.1103/PhysRevLett. Introductory textbooks • I. 315–321. pp. • F.D.W.D. Gripaios (2006). Bibcode:1977PhLB.1016/j. “Standard Model: An Introduction”. Bibcode:1973PhR.44.1529H.1016/03702693(77)90435-X. B. Hey (2003). Abers. Oerter (2006). Griffiths (1987). ISBN 0-19-851961-3. “The Universe Is A Strange Place”.4. Institute of Physics.M. L.1.. Greiner. J.. (2012). • W.. Bibcode:2004NuPhS. ISBN 0-52134785-8. (1999). B." New Scientist. doi:10. Cheng.1007/JHEP06(2014)080. Oxford University Press. arXiv:astroph/0401347. E..J. Highlights the gauge theory • "The Standard Model explained in Detail by aspects of the Standard Model. Müller (2000). Lee (1973). Modern Elementary Particle Physics. Baak et al. • "LHC sees hint of lightweight Higgs boson" "New Scientist". “Gauge theories”. Elementary Particle Physics: Foundations of the Standard Model. ISBN 0-201-11749-5. Hayato et al.nuclphysbps. .11 Further reading • R. arXiv:hepex/9904020. • "Standard Model may be found incomplete. Golowich. doi:10. ISBN 978-0-521-47652-2.1140/epjc/s10052-012-2205-9.421M. O'Raifeartaigh (1988). doi:10.. JHEP 1406 (2014) 080. ISBN 0-471-603864.080S. Z. Holstein (1994). ISBN 978-0-585-44550-2. (CRC Press. arXiv:1403.3W.. Bibcode:1999PhRvL. • J. Dynamics of the Standard Model.912M.83. Volume 2. Cambridge University Press. [37] M. Cambridge University Press.A. Bibcode:2012EPJC.Proceedings Supplements 134: 3. Highlights dynamical and phenomenological aspects of the Standard Model. B. M. Dodd..08.9. Coughlan.P. 4. arXiv:1209. the Unsung Triumph of Modern Physics.06. ISBN 0-444-85438-X. STANDARD MODEL [35] P. Ramond and R. doi:10. Journal articles • E.S. Perseus Books.1A. • G.F. The Ideas of Particle Physics: An Introduction for Scientists. • Y.F. Schumm (2004). N. doi:10. • D. Bibcode:2014JHEP.912. Introduction to Elementary Particles. • M. ISBN 0-8018-7971-X. Advanced textbooks 65 • L. Plume.1103/PhysRevLett. (Wiley 2013) 920 рапуы • Schwartz. • D... Freedman. • G. “The Electroweak Fit of the Standard Model after the Discovery of a New Boson at the LHC”.1529. Strumia (2014-03-17). CERN’s John Ellis" omega tau podcast. Bibcode:1980PhRvL.... The European Physical Journal C 72 (11).. [36] R. Nuclear Physics B . Group structure of gauge theories. arXiv:hep-ph/0001283 [hep-ph].83. Novaes (2000). A.F.67. Physical Review Letters 83 (8): 1529. Gell-Mann.E.72. The Theory of Almost Everything: The Standard Model.. [38] Salvio. Supergravity. Kane (1987). Deep Down Things: The Breathtaking Beauty of Particle Physics. Physics Letters B 67 (4): 421. • T. “Neutrino Mass and Spontaneous Parity Nonconservation”. P. “Agravity”. F. arXiv:hep-ph/9912523 [hep-ph]. 2010) 670 pages Highlights grouptheoretical aspects of the Standard Model. doi:10. Mohapatra. Li (2006). B.. ed.R. John Wiley & Sons.. Slansky (1979).134. Physics Reports 9: 1–141. doi:10.44.1.2205B. or even household dust).quantum physics culminated in proofs of nuclear fission ality. unique type of particle. and nuclear fusion by Hans Bethe in that same In more technical terms. made of quarks). measurements of neutrino mass have provided the and the fundamental fields that must be defined in order first experimental deviations from the Standard Model. the term elementary particles is applied to those particles that are. but physicists soon discovered that atoms are not. • "The Standard Model Lagrangian. Dynamics of particles is also governed early 20th-century explorations of nuclear physics and by quantum mechanics. can be described almost entirely by a quantum field theelsewhere. However. accounting for the hundreds of other species usually referred to as matter . Matthew (2002) “Introduction to the Standard Model of Particle Physics” on Kuro5hin: Part 1.[4] The Standard Model. In recent physics” usually refers to the study of “smallest” particles years. as well as a wide range of ates of even smaller particles. and of particles that have been discovered since the 1960s. • "The Standard Model" The Standard Model on the The particle content of the Standard Model of Physics CERN web site explains how the basic building blocks of matter interact. Hahn). and neutrons (protons and neutrons are com. according to current understanding. the term “particle awaits discovery (See Theory of Everything). neutrinos. displaying particle-like behavior under certain ex. such as fact. with the recent finding of Higgs boson. such as the electron. and that a more fundamental theory gas particle. a be- .in 1939 by Lise Meitner (based on experiments by Otto perimental conditions and wave-like behavior in others.massless particles. The exotic particles. Following the convention of particle physicists.[1][2] The idea that all matter is composed of elementary particles dates to at least the 6th century BC. therefore particle physics is largely the study of the Standard Main article: History of subatomic physics Model’s particle content and its possible extensions.2. through his work on stoichiometry.then. quantum field theory. see particle (disambiguation).2 Particle physics of other particles. and LaTeX versions.1 Subatomic particles concluded that each element of nature was composed of Modern particle physics research is focused on subatomic a single. Part 3b. radiation . PDF. afparticles.[3] Particle physics is a branch of physics which studies the Those elementary particles can combine to form composnature of particles that are the constituents of what is ite particles." Web tutorial. the fundamental particles of nature. to explain the observed particles.[3] For other uses of the word “particle” in physics and All particles. deprotons. ter the Greek word atomos meaning “indivisible”. governed by four fundamental forces. The Standard Model has been found to agree with almost particles are excitations of quantum fields and interact folall the experimental tests conducted to date.notes the smallest particle of a chemical element since posite particles called baryons. Throughout the 1950s and 1960s.2 History summarized in a theory called the Standard Model. These cannot be defined by a combination of other fundamental fields. a proton. Although the word "particle" can most particle physicists believe that it is an incomplete debe used in reference to many objects (e. ory called the Standard Model. they exhibit wave–particle du. with no explicit Higgs boson.66 CHAPTER 4.particles with mass. • "Standard Model Lagrangian" with explicit Higgs terms. • "The particle adventure. lowing their dynamics. 4. but conglomerphotons. which is also treated in nuclear weapons.g. in duced by radioactive and scattering processes. and muons. John Dalton. they are described by quantum year.2. • Nobes. pro. a scription of nature. PostScript. and their interactions observed to date. THEORY • "Observation of the Top Quark" at Fermilab. Part 3a.[6] The word atom. presumed to be indivisible and not composed 4." After electroweak symmetry breaking. including atomic constituents such as electrons. as currently formulated. both discoveries also led to the development of state vectors in a Hilbert space. In current understanding. The current set of fundamental fields and their dynamics are 4.[5] In the 19th century. has 61 elementary particles. Part 2. 4.2. PARTICLE PHYSICS wildering variety of particles were found in scattering experiments. It was referred to as the "particle zoo". That term was deprecated after the formulation of the Standard Model during the 1970s in which the large number of particles was explained as combinations of a (relatively) small number of fundamental particles. 4.2.3 Standard Model Main article: Standard Model The current state of the classification of all elementary particles is explained by the Standard Model. It describes the strong, weak, and electromagnetic fundamental interactions, using mediating gauge bosons. The species of gauge bosons are the gluons, W−, W+ and Z bosons, and the photons.[4] The Standard Model also contains 24 fundamental particles, (12 particles and their associated anti-particles), which are the constituents of all matter.[7] Finally, the Standard Model also predicted the existence of a type of boson known as the Higgs boson. Early in the morning on 4 July 2012, physicists with the Large Hadron Collider at CERN announced they have found a new particle that behaves similarly to what is expected from the Higgs boson.[8] 4.2.4 Experimental laboratories In particle physics, the major international laboratories are located at the: • Brookhaven National Laboratory (Long Island, United States). Its main facility is the Relativistic Heavy Ion Collider (RHIC), which collides heavy ions such as gold ions and polarized protons. It is the world’s first heavy ion collider, and the world’s only polarized proton collider.[9] • Budker Institute of Nuclear Physics (Novosibirsk, Russia). Its main projects are now the electronpositron colliders VEPP-2000,[10] operated since 2006, and VEPP-4,[11] started experiments in 1994. Earlier facilities include the first electron-electron beam-beam collider VEP-1, which conducted experiments from 1964 to 1968; the electron-positron colliders VEPP-2, operated from 1965 to 1974; and, its successor VEPP-2M,[12] performed experiments from 1974 to 2000.[13] • CERN, (Conseil Européen pour la Recherche Nucléaire) (Franco-Swiss border, near Geneva). Its main project is now the Large Hadron Collider (LHC), which had its first beam circulation on 10 September 2008, and is now the world’s most energetic collider of protons. It also became the most energetic collider of heavy ions after it began colliding lead ions. Earlier facilities include the 67 Large Electron–Positron Collider (LEP), which was stopped on 2 November 2000 and then dismantled to give way for LHC; and the Super Proton Synchrotron, which is being reused as a pre-accelerator for the LHC.[14] • DESY (Deutsches Elektronen-Synchrotron) (Hamburg, Germany). Its main facility is the Hadron Elektron Ring Anlage (HERA), which collides electrons and positrons with protons.[15] • Fermi National Accelerator Laboratory (Fermilab), (Batavia, United States). Its main facility until 2011 was the Tevatron, which collided protons and antiprotons and was the highest-energy particle collider on earth until the Large Hadron Collider surpassed it on 29 November 2009.[16] • KEK, (Tsukuba, Japan). It is the home of a number of experiments such as the K2K experiment, a neutrino oscillation experiment and Belle, an experiment measuring the CP violation of B mesons.[17] • SLAC National Accelerator Laboratory, (Menlo Park, United States). Its 2-mile-long linear particle accelerator began operating in 1962 and was the basis for numerous electron and positron collision experiments until 2008. Since then the linear accelerator is being used for the Linac Coherent Light Source X-ray laser as well as advanced accelerator design research. SLAC staff continue to participate in developing and building many particle physics experiments around the world.[18] Many other particle accelerators do exist. The techniques required to do modern, experimental, particle physics are quite varied and complex, constituting a sub-specialty nearly completely distinct from the theoretical side of the field. 4.2.5 Theory Theoretical particle physics attempts to develop the models, theoretical framework, and mathematical tools to understand current experiments and make predictions for future experiments. See also theoretical physics. There are several major interrelated efforts being made in theoretical particle physics today. One important branch attempts to better understand the Standard Model and its tests. By extracting the parameters of the Standard Model, from experiments with less uncertainty, this work probes the limits of the Standard Model and therefore expands our understanding of nature’s building blocks. Those efforts are made challenging by the difficulty of calculating quantities in quantum chromodynamics. Some theorists working in this area refer to themselves as phenomenologists and they may use the tools of quantum field theory and effective field theory. Others 68 CHAPTER 4. THEORY make use of lattice field theory and call themselves lattice theorists. energy scales. Furthermore, there may be surprises that will give us opportunities to learn about nature. Another major effort is in model building where model builders develop ideas for what physics may lie beyond the Standard Model (at higher energies or smaller distances). This work is often motivated by the hierarchy problem and is constrained by existing experimental data. It may involve work on supersymmetry, alternatives to the Higgs mechanism, extra spatial dimensions (such as the Randall-Sundrum models), Preon theory, combinations of these, or other ideas. Much of the effort to find this new physics are focused on new collider experiments. The Large Hadron Collider (LHC) was completed in 2008 to help continue the search for the Higgs boson, supersymmetric particles, and other new physics. An intermediate goal is the construction of the International Linear Collider (ILC), which will complement the LHC by allowing more precise measurements of the properties of newly found particles. In August 2004, a decision for the technology of the ILC was A third major effort in theoretical particle physics is taken but the site has still to be agreed upon. string theory. String theorists attempt to construct a uni- In addition, there are important non-collider experiments fied description of quantum mechanics and general rel- that also attempt to find and understand physics beyond ativity by building a theory based on small strings, and the Standard Model. One important non-collider effort branes rather than particles. If the theory is successful, it is the determination of the neutrino masses, since these may be considered a "Theory of Everything", or “TOE”. masses may arise from neutrinos mixing with very heavy There are also other areas of work in theoretical particle particles. In addition, cosmological observations provide physics ranging from particle cosmology to loop quantum many useful constraints on the dark matter, although it may be impossible to determine the exact nature of the gravity. dark matter without the colliders. Finally, lower bounds This division of efforts in particle physics is reflected on the very long lifetime of the proton put constraints on in the names of categories on the arXiv, a preprint Grand Unified Theories at energy scales much higher than archive:[19] hep-th (theory), hep-ph (phenomenology), collider experiments will be able to probe any time soon. hep-ex (experiments), hep-lat (lattice gauge theory). In May 2014, the Particle Physics Project Prioritization Panel released its report on particle physics funding priorities for the United States over the next decade. This re4.2.6 Practical applications port emphasized continued U.S. participation in the LHC and ILC, and expansion of the Long Baseline Neutrino In principle, all physics (and practical applications devel- Experiment, among other recommendations. oped therefrom) can be derived from the study of fundamental particles. In practice, even if “particle physics” is In early October 2014 the LHC discovered a new partaken to mean only “high-energy atom smashers”, many ticle that was found to have four quarks, named the [21] technologies have been developed during these pioneer- tetraquark. ing investigations that later find wide uses in society. Cyclotrons are used to produce medical isotopes for re4.2.8 See also search and treatment (for example, isotopes used in PET imaging), or used directly for certain cancer treatments. • Atomic physics The development of Superconductors has been pushed forward by their use in particle physics. The World Wide • High pressure Web and touchscreen technology were initially developed • International Conference on High Energy Physics at CERN. Additional applications are found in medicine, national security, industry, computing, science, and workforce development, illustrating a long and growing list of beneficial practical applications with contributions from particle physics.[20] • Introduction to quantum mechanics • List of accelerators in particle physics • List of particles • Magnetic monopole 4.2.7 Future • Micro black hole • Number theory The primary goal, which is pursued in several distinct ways, is to find and understand what physics may lie beyond the standard model. There are several powerful experimental reasons to expect new physics, including dark matter and neutrino mass. There are also theoretical hints that this new physics should be found at accessible • Resonance (particle physics) • Self-consistency principle in high energy Physics • Non-extensive self-consistent thermodynamical theory 4.2. PARTICLE PHYSICS 69 • Standard Model (mathematical formulation) [19] arxiv.org • Stanford Physics Information Retrieval System [20] “Fermilab | Science at Fermilab | Benefits to Society”. Fnal.gov. Retrieved 23 June 2012. • Timeline of particle physics [21] “Universe Today; Benefits to Society”. Universe Today. Retrieved 8 October 2014. • Unparticle physics • Tetraquark 4.2.9 4.2.10 Further reading References Introductory reading [1] http://home.web.cern.ch/topics/higgs-boson [2] http://www.nobelprize.org/nobel_prizes/physics/ laureates/2013/advanced-physicsprize2013.pdf • Close, Frank (2004). Particle Physics: A Very Short Introduction. Oxford University Press. ISBN 0-19280434-0. [3] Braibant, S.; Giacomelli, G.; Spurio, M. (2009). Particles and Fundamental Interactions: An Introduction to Particle Physics. Springer. pp. 313–314. ISBN 978-94-0072463-1. • Close, Frank; Marten, Michael; Sutton, Christine (2004). The Particle Odyssey: A Journey to the Heart of the Matter. Oxford University Press. ISBN 9780198609438. [4] “Particle Physics and Astrophysics Research”. The Henryk Niewodniczanski Institute of Nuclear Physics. Retrieved 31 May 2012. • Ford, Kenneth W. (2005). The Quantum World. Harvard University Press. [5] “Fundamentals of Physics and Nuclear Physics” (PDF). Retrieved 21 July 2012. [6] “Scientific Explorer: Quasiparticles”. Sciexplorer.blogspot.com. 22 May 2012. Retrieved 21 July 2012. [7] Nakamura, K (1 July 2010). “Review of Particle Physics”. Journal of Physics G: Nuclear and Particle Physics 37 (7A): 075021. Bibcode:2010JPhG...37g5021N. doi:10.1088/0954-3899/37/7A/075021. [8] Mann, Adam (28 March 2013). “Newly Discovered Particle Appears to Be Long-Awaited Higgs Boson - Wired Science”. Wired.com. Retrieved 6 February 2014. [9] “Brookhaven National Laboratory – A Passion for Discovery”. Bnl.gov. Retrieved 23 June 2012. [10] “index”. Vepp2k.inp.nsk.su. Retrieved 21 July 2012. [11] “The VEPP-4 accelerating-storage V4.inp.nsk.su. Retrieved 21 July 2012. complex”. [12] “VEPP-2M collider complex” (in Russian). Inp.nsk.su. Retrieved 21 July 2012. [13] “The Budker Institute Of Nuclear Physics”. English Russia. 21 January 2012. Retrieved 23 June 2012. [14] “Welcome to”. Info.cern.ch. Retrieved 23 June 2012. [15] “Germany’s largest accelerator centre – Deutsches Elektronen-Synchrotron DESY”. Desy.de. Retrieved 23 June 2012. [16] “Fermilab | Home”. Fnal.gov. Retrieved 23 June 2012. [17] “Kek | High Energy Accelerator Research Organization”. Legacy.kek.jp. Retrieved 23 June 2012. [18] http://www6.slac.stanford.edu/. Retrieved 19 February 2015. Missing or empty |title= (help) • Oerter, Robert (2006). The Theory of Almost Everything: The Standard Model, the Unsung Triumph of Modern Physics. Plume. • Schumm, Bruce A. (2004). Deep Down Things: The Breathtaking Beauty of Particle Physics. Johns Hopkins University Press. ISBN 0-8018-7971-X. • Close, Frank (2006). The New Cosmic Onion. Taylor & Francis. ISBN 1-58488-798-2. Advanced reading • Robinson, Matthew B.; Bland, Karen R.; Cleaver, Gerald. B.; Dittmann, Jay R. (2008). “A Simple Introduction to Particle Physics”. arXiv:0810.3328 [hep-th]. • Robinson, Matthew B.; Cleaver, Gerald; Cleaver, Gerald B. (2009). “A Simple Introduction to Particle Physics Part II”. arXiv:0908.1395 [hep-th]. • Griffiths, David J. (1987). Introduction to Elementary Particles. Wiley, John & Sons, Inc. ISBN 0471-60386-4. • Kane, Gordon L. (1987). Modern Elementary Particle Physics. Perseus Books. ISBN 0-201-11749-5. • Perkins, Donald H. (1999). Introduction to High Energy Physics. Cambridge University Press. ISBN 0521-62196-8. • Povh, Bogdan (1995). Particles and Nuclei: An Introduction to the Physical Concepts. Springer-Verlag. ISBN 0-387-59439-6. • Boyarkin, Oleg (2011). Advanced Particle Physics Two-Volume Set. CRC Press. ISBN 978-1-43980412-4. ).1103/Physics.. unbroken symmetry of nature. a photon would have two fermion superpartners and a scalar su. these particles are often referred to as axinos and saxions. . no such ev[4] • CERN – European Organization for Nuclear Re. but no superpartners. Sprouse.70 4.3 See also sored by the Particle Data Group of the Lawrence • Chargino Berkeley National Laboratory (LBNL) • Gluino 4. Retrieved 21 February 2011. The New York Times (Manhattan. New York: Arthur Ochs Sulzberger. Part 3b. This may indicate that supersymmetry is incorrect. and each boson should have a partner fermion.5 External links perpartner. Gene D.4 supersymmetry and particle.98L.[1][2] • Neutralino • Sfermion • Higgsino The word superpartner is a portmanteau of supersymmetry and partner. Scientific American (Nature Publishing Group).4. New Scientist. ISSN 0036-8733.11 CHAPTER 4. Archived from the original on 2011-02-22. doi:10. it should be possible to recreate these particles in high-energy particle ac• Fermilab celerators.[1] • Nobes. Doing so will not be an easy task. with two copies of supersymmetry in four dimensions. “Meet a superpartner at the LHC”. Paul (November 22. “Sidebar: Solving the Higgs Puzzle”. real scalar field. “A Giant Takes On Physics’ Biggest Questions”.3. 4. p. Retrieved 20 December 2013. there is a fermion superpartner as well as a second.3.3. Retrieved 21 February 2011. For instance. Archived from the original on 2011-02-22. F1.3. “Higgs Nobel bash: I was at the party of the universe”. the fermion’s superpartner. [2] Overbye.[1] However. Bibcode:2010PhyOJ. [4] Jamieson. THEORY External links 4.98.idence has been found. 2010).. Matthew (2002) “Introduction to the Stan.[1][3] For particles that are real scalars (such as an axion). Part 2.4. [3] Quigg. ed. Chris (January 17. each fermion should have a partner boson. OCLC 1775222.Some researchers have hoped the Large Hadron Collider dard Model of Particle Physics” on Kuro5hin: Part at CERN might produce evidence for the existence of su1. or it may also be the result of the fact that supersymmetry is not an exact. their masses would indicate the scale at which supersymmetry is broken. Part 3a.3. ISSN 1943-2879. If superpartners are found. these partitimes greater than • Particle physics – it matters – the Institute of Physics cles may have masses up to a thousand their corresponding “real” particles.2 Recreating superpartners • Symmetry magazine If the supersymmetry theory is correct.. ISSN 0362-4331.1 Theoretical predictions According to the supersymmetry theory.. Exact unbroken supersymmetry would predict that a particle and its superpartners would have the same mass. Retrieved 21 February 2011.2. Supersymmetry is one of the synergistic theories in current high-energy physics that predicts the existence of these “shadow” particles.3 Superpartner • Gravitino as a superpartner of the hypothetical graviton In particle physics. The word sparticle is a portmanteau of 4. Physics (New York: American Physical Society) 3 (98). Dennis (May 15.3. search • The Particle Adventure – educational project spon. For axions. OCLC 233971234. However. So far the Higgs hasn't given many supersymmetric clues. a superpartner (also sparticle) is a hypothetical elementary particle. References [1] Langacker. No superpartners of the Standard Model particles have yet been found.3. 2007). Valerie (13 December 2013). perpartner particles. 2008). OCLC 1645522. • Argonne National Laboratory In zero dimensions it is possible to have supersymmetry. In extended supersymmetry there may be more than one superparticle for a given particle. this is the only situation • Large Hadron Collider where supersymmetry does not imply the existence of su• CERN homepage perpartners.. Jr. as of 2013. and biguation).[14][15] critical phenomena. but there has been still no evidence of them. since it leaves gravitation crossroad in theoretical (and particle) physics.[4] There is definitive observation of a Strange B meson decaying into only indirect evidence for the existence of supersymme.The first realistic supersymmetric version of the Standard Model was proposed in 1977 by Pierre Fayet and is called iments with the Large Hadron Collider also yielded extremely rare particle decay events which casts doubt on the Minimal Supersymmetric Standard Model or MSSM for short.tween elementary particles of different quantum nature. . which establishes a relationship beinteger spin.Miyazawa in 1966.collisions and offers the best chance at discovering superciple. Schwarz and would have the same mass energy and thus be equally André Neveu. symmetries in that it establishes a symmetry between signs of the suclassical and quantum physics. supersymmetry (SUSY) is a pro. in a variety of fields.Salam and their fellow researchers introduced early parlem. A. and string theory by Pierre Ramond. The Minimal Supersymmetric Standard Model is ticle physics applications.V. supersymmetry must be a Finally.symmetries of the microscopic world. But particles for the foreseeable future. For other uses.4. as any superpartners that exist would now need to be too massive to solve the paradoxes anyway. The Large Hadron been observed in any other domain. While any numCollider at CERN is producing the world’s highest-energy ber of bosons can occupy the same quantum state. it would explain many gled them out as remarkable QFTs.P. Sakita (in 1971). since no superpart[13] identiners have been observed yet. Supersymmetry fectly unbroken supersymmetry. each pair of superpart. That makes it difficult to expect that bosons pos. In a theory with per.[3] and predicts superpartners with masses between 100 GeV Supersymmetry differs notably from currently known and 1 TeV. quantum After the discovery of the Higgs particle in 2012. which allows only one fermion in a given state. was badly broken. The mathematical structure one of the best studied candidates for physics beyond the of supersymmetry (Graded Lie superalgebras) has subsequently been applied successfully to other areas of Standard Model. and that they are at a unification of all interactions. GolSupersymmetry (Angel) fand and E. a radically new type of symmetry of spacetime and an integer-valued spin.and V.4. this refers only to electroweak Neil Turok at Perimeter Institute concedes that theorists and strong interactions and does not provide the ultimate are disheartened at that situation. ated with a particle from the other. It was proposed to solve the hierarchy problem many versions of supersymmetry. fermions do CERN. and they and Abdus mysterious features of particle physics and would help solve paradoxes such as the cosmological constant prob. ranging from nuclear The failure of the Large Hadron Collider to find evidence physics.[6][7][8][9] For the episode of the American TV series Angel. by Hironari “SUSY” redirects here. This supersymmetry did not involve spacetime. Gervais and B. no meaningful [17][18] perpartners have been observed. that is it concerned internal symmetry. It remains a vital part of many the theory should be abandoned as a solution to such prob.[1] Each particle from one group is associ.fundamental fields. see J. easy to find in the lab.[19] unification. see Susy (disam. which have a half. He described the LHC results as “simple. which up to now has not As of September 2011. The not. confirming a standard model prediction.4. P.with a consistent Lie-algebraic graded structure on which ners shares the same mass and internal quantum numbers the Gervais−Sakita rediscovery was based directly first besides spin – for example. Wess and B.LHCb and CMS experiments at the LHC made the first sess the same quantum numbers as fermions. when the occupation numbers become large. Likhtman (also in 1971). bosons and fermions. Volkov In particle physics. J. physics. called its superpartner. SUPERSYMMETRY 4. a “selectron” (superpartner arose in 1971[12] in the context of an early version of electron) would be a boson version of the electron.4 Supersymmetry 71 4. but try. L.[2] Exper. and fermions. Akulov (in 1972). deep crisis.1 History A supersymmetry relating mesons and baryons was first proposed. and D. This means that expected that supersymmetric particles would be found at while bosons also exist in classical physics. His work was largely ignored at the time. However. If supersymdimensional supersymmetric field theories.[16] quantum mechanfor supersymmetry has led some physicists to suggest that ics to statistical physics. it was physics approaches the classical limit. calling it a untouched. primarily in the form of evidence for gauge coupling a blow for those hoping for signs of supersymmetry. lems. for fermions this is not possible because of the exclusion prin. which sinmetry is a true symmetry of nature.[11] independently rediscovposed extension of spacetime symmetry that relates two ered supersymmetry in the context of quantum field thebasic classes of elementary particles: bosons. John H.[10] Yu.proposed theories of physics. and unifies spacetime and internal whose spin differs by a half-integer. Zumino (in 1974) fied the characteristic renormalization features of fourspontaneously broken symmetry if it exists.two muons. in the context of hadronic physics.[5] However. which have ory. In 1975 the Haag-Lopuszanski-Sohnius theorem analyzed all possible superalgebras in the general form.72 CHAPTER 4. on the other hand. has the following anti-commutation problems become exactly solvable.[17][18] which is beginning to significantly constrain the most popular incarnations of supersymmetry. THEORY yet extremely puzzling” and said “we have to get peo. Pµ = −i∂ µ are the generators of Mandula theorem. and the result is said to be a theory of supergravity. It is also a neces¯˙ = 2(σ µ ) ˙ Pµ αβ sary feature of the most popular candidate for a theory of {Qα .3 Applications ple to try to find the new principles that will explain the simplicity”.[24] There are representations of a Lie superalgebra that are analogous to representations of a Lie algebra. Another theoretically appealing property of supersym. This extended superPoincaré algebra paved the way for obtaining a very large and important class of supersymmetric field theories. In 1971 Golfand and Likhtman were the first to show that the Poincaré algebra can be extended through introduction of four anticommuting spinor generators (in four dimensions). According to the spin-statistics theorem. which prohibits spacetime and internal In the above expression µ Pauli matrices. Combining the two kinds of fields into a single algebra requires the introduction of a Z2 -grading under which the bosons are the even elements Supersymmetry is also motivated by solutions to several and the fermions are the odd elements. translation and σ are the symmetries from being combined in any nontrivial way. Such an algebra theoretical problems. the strong and electromagnetic interactions. the Higgs boson mass is subject to quantum corrections which are so large as to naturally drive it close to the Planck mass barring its fine tuning to an extraordinarily tiny value. these quantum corrections are canceled by those from the corresponding superpartners above the supersymmetry breaking scale. When supersymme.4. the conformal group with a compact internal symmetry group.relation: try is imposed as a local symmetry.and all other anti-commutation relations between the Qs metry is that it offers the only “loophole” to the Coleman– and commutation relations between the Qs and Ps vanish.[21][22] provides a natural mechanism for electroweak symmetry breaking and allows for the precise high-energy unification of the weak. superstring theory. no meaningful signs of the superpartners have been observed.[23] These scenarios would imply that experimental traces of the superpartners should begin to emerge in high-energy collisions at the LHC relatively soon. Einstein’s theory of general relativity is included automatically.4.[20] Extension of possible symmetry groups 4. Expressed in terms field theory is often much easier to analyze. Supersymmetric quantum algebra is the Super-Poincaré algebra. the symmetries of the S-matrix must be a direct product of the Poincaré group with a compact internal symmetry group or if there is no mass gap. for generally providing many de. which becomes the new characteristic natural scale for the Higgs mass. bosonic fields commute while fermionic fields anticommute. on the other hand. In the supersymmetric theory. The Haag-LopuszanskiSohnius theorem demonstrates that supersymmetry is the only way spacetime and internal symmetries can be consistently combined. the total parameter space of consistent supersymmetric extensions of the Standard Model is extremely diverse and can not be definitively ruled out at the LHC.2 Motivations A central motivation for supersymmetry close to the TeV energy scale is the resolution of the hierarchy problem of the Standard Model. These symmetries are grouped into the Poincaré group and internal symmetries and the Coleman–Mandula theorem showed that under certain assumptions. However. Supersymmetries. for quantum field theories like the Standard Model under very general assumptions. as many more of two Weyl spinors. which later became known as supercharges.is called a Lie superalgebra. sirable mathematical properties. The supersymmetry Supersymmetry algebra algebra Main article: Traditional symmetries in physics are generated by objects that transform under the tensor representations of the Poincaré group and internal symmetries.The simplest supersymmetric extension of the Poincaré ble behavior at high energies. and for ensuring sensi. As of September 2011. Q β} everything. Without the extra supersymmetric particles.4. Each Lie algebra has an associated Lie group and a Lie superalgebra can sometimes be extended into representations of a Lie supergroup. One reason that physicists explored supersymmetry is because it offers an extension to the more familiar symmetries of quantum field theory. scenarios where supersymmetric partners appear with masses not much greater than 1 TeV are considered the most wellmotivated by theorists. . Therefore. including those with an extended number of the supergenerators and central charges. are generated by objects that transform under the spinor representations. Other attractive features of TeV-scale supersymmetry are the fact that it often provides a candidate dark matter particle at a mass scale consistent with thermal relic abundance calculations. Supersymmetry reduces the size of the quantum corrections by having automatic cancellations between fermionic and bosonic Higgs interactions. The only constraint on this new sector is that it must break supersymmetry permanently and must give superparticles TeV scale masses. The simplest possible supersymmetric model consistent with the Standard Model is the Minimal Supersymmetric Standard Model (MSSM) which can include the necessary additional new particles that are able to be superpartners of those in the Standard Model. 73 of the theory does not respect the symmetry and supersymmetry is broken spontaneously. In many supersymmetric Standard Models there is a heavy stable particle (such as neutralino) which could serve as a weakly interacting massive particle (WIMP) dark matter candidate. the natural size of the Higgs mass is the highest scale possible. With the addition of new particles. there are many possible new interactions. The SUSY partner of this Hamiltonian would be “fermionic”. arbitrary soft SUSY breaking terms are added to the theory which temporarily break SUSY explicitly but could never arise from a complete theory of supersymmetry breaking. The renormalization group evolution of the three gauge coupling constants of the Standard Model is somewhat sensitive to the present particle content of the theory. which are called partner Hamiltonians. This problem is known as the hierarchy problem. and its . SUPERSYMMETRY The Supersymmetric Standard Model Main article: Minimal Supersymmetric Standard Model Incorporating supersymmetry into the Standard Model requires doubling the number of particles since there is no way that any of the particles in the Standard Model can be superpartners of each other. (The potential energy terms which occur in the Hamiltonians are then called partner potentials. The existence of a supersymmetric dark matter candidate is closely tied to R-parity. These coupling constants do not quite meet together at a common energy scale if we run the renormalization group using the Standard Model. It is analogous to the original description of SUSY. The standard paradigm for incorporating supersymmetry into a realistic theory is to have the underlying dynamics of the theory be supersymmetric.4. We can imagine a “bosonic Hamiltonian”. then the Higgs mass is related to supersymmetry breaking which can be induced from small non-perturbative effects explaining the vastly different scales in the weak interactions and gravitational interactions. SUSY quantum mechanics involves pairs of Hamiltonians which share a particular mathematical relationship.[5] With the addition of minimal SUSY joint convergence of the coupling constants is projected at approximately 1016 GeV.[5] Cancellation of the Higgs boson quadratic mass renormalization between fermionic top quark loop and scalar stop squark tadpole Feynman diagrams in a supersymmetric extension of the Standard Model Supersymmetric quantum mechanics Main article: Supersymmetric quantum mechanics One of the main motivations for SUSY comes from the quadratically divergent contributions to the Higgs mass squared. The supersymmetry break can not be done permanently by the particles of the MSSM as they currently appear. This means that there is a new sector of the theory that is responsible for the breaking.) An introductory theorem shows that for every eigenstate of one Hamiltonian. Gauge-coupling unification Main article: Minimal Supersymmetric Standard Model § Gauge-coupling unification One piece of evidence for supersymmetry existing is gauge coupling unification. The quantum mechanical interactions of the Higgs boson causes a large renormalization of the Higgs mass and unless there is an accidental cancellation. If supersymmetry is restored at the weak scale. There are many models that can do this and most of their details do not matter. This fact can be exploited to deduce many properties of the eigenstate spectrum. In order to parameterize the relevant features of supersymmetry breaking. and due to the simplified nature of having fields which are only functions of time (rather than space-time). its partner Hamiltonian has a corresponding eigenstate with the same energy. but the ground state Supersymmetric quantum mechanics adds the SUSY superalgebra to quantum mechanics as opposed to quantum field theory.4. whose eigenstates are the various bosons of our theory. which referred to bosons and fermions. a great deal of progress has been made in this subject and it is now studied in its own right. Supersymmetric quantum mechanics often comes up when studying the dynamics of supersymmetric solitons. This corresponds to an N = 8 supersymmetry theory. Typically the number of copies of a supersymmetry is a power of 2. i. whenever they are not invariant under such symmetry) • N=1 Chiral multiplet: (0. 2.1) supergravity multiplet: (1. which allows holomorphic quantities to be exactly computed.4 General supersymmetry would have a fermionic partner of equal energy. The use of the supersymmetry method provides a mathematical rigorous alternative to the replica trick. SUSY transformations have been also proposed as a way to address inverse scattering problems in optics and as a onedimensional transformation optics [28] Extended supersymmetry Main article: Extended supersymmetry It is possible to have more than one kind of supersymmetry transformation. In addition.2) • N=2 Mathematics hypermultiplet: (-1 ⁄2 .3 ⁄2 2 . Theories with more than 32 supersymmetry generators automatically have massless fields with spin greater than 2. ⁄2 . A prime example of this has been tiplet: (0.1 ⁄2 2 . 8.1 . ⁄2 . The Fokker-Planck equation being an example of a nonquantum theory.1 ⁄2 ) vector multiplet: (0. In four dimensions. It is possible to have multiple supersymmetries and also have superSupersymmetry: Applications to condensed matter symmetric extra dimensions. with the corresponding multiplets[30] (CPT adds a copy. The `supersymmetry' in all these systems arises from the fact that one is modelling one particle and as such the`statistics’ don't matter. a spinor has four degrees of freedom and thus the minimal number of supersymmetry generators is four in four dimensions and having eight copies of supersymmetry means that there are 32 supersymmetry generators. Along these lines. It is not known how to make massless fields with spin greater than two interact.1) Supergravity mul1 4 6 3 4 more realistic theories. This is because it describes complex • N=4 fields satisfying a property known as holomorphy. physics SUSY concepts have provided useful extensions to the WKB approximation. but only in non-interacting systems. the more constrained the field content and interactions are. SUSY has been applied to disorder averaged systems both quantum and non-quantum (through statistical mechanics).3 ⁄2 ) Graviton multiplet: (3 ⁄2 . so the maximal number of supersymmetry generators considered is 32. ⁄2 .4. ⁄2 .−128 .0 . Theories with more than one supersymmetry transformation are known as extended supersymmetric theories.1 ⁄2 ) Vector multiplet: (1 ⁄2 . For more on the applications of supersymmetry in condensed matter physics see the book[25] Supersymmetry in optics Integrated optics was recently found[26] to provide a fertile ground on which certain ramifications of SUSY can be explored in readily-accessible laboratory settings.-3 ⁄2 8 . ⁄2 .74 CHAPTER 4..1) Gravitino multiplet: (1.2) SUSY is also sometimes studied mathematically for its intrinsic properties. mode conversion[27] and space-division multiplexing becomes possible. Supersymmetry appears in many different contexts in theoretical physics that are closely related. The more supersymmetry a theory has. Each boson 4.1 . In four dimensions there are the following theories. ⁄2 . THEORY eigenstates would be the theory’s fermions.02 .- .⁄2 . 1 4 6 1 4 This makes supersymmetric models useful toy models of Vector multiplet: (−1. a new class of functional optical structures with possible applications in phase matching.Supergravity multiplet: 1 56 70 1 56 28 3 8 chanics. one may interpret the refractive index distribution of a structure as a potential landscape in which optical wave packets propagate.e. • N=8 The proof of the Atiyah-Singer index theorem is much simplified by the use of supersymmetric quantum me. which attempts to address the so-called `problem of the denominator' under disorder averaging. 1. The maximal number of supersymmetry generators possible is 32. Making use of the analogous mathematical structure of the quantum-mechanical Schrödinger equation and the wave equation governing the evolution of light in onedimensional settings.0 .2) the demonstration of S-duality in four-dimensional gauge theories[29] that interchanges particles and monopoles. Theories with 32 supersymmetries automatically have a graviton.2) (−2. 4. has proposed that a loop quantum gravity theory incorporating either supersymmetry or exIt is possible to have supersymmetry in dimensions other tra dimensions.6 Supersymmetry in quantum gravity SUSY is often criticized in that its greatest strength and weakness is that it is not falsifiable. the greatest number of di. Two of the most active approaches to forming a theory of quantum gravity are string theory and loop quantum gravity (LQG).From 2003. If the Large Hadron Collider and other major particle physics experiments fail to 4. WMAP's dark matter density measurements ory. and provides a palette of fundamental particles upon which all four forces act. or both. 4.4. the WMAP dark matter denbroken symmetry). SUPERSYMMETRY 75 Supersymmetry in alternate numbers of dimensions originators of LQG. which would unify the classical theory of general relativity and the Standard Model.4. Supersymmetry is part of a larger enterprise of theoretical physics to unify everything we know about the physical world into a single fundamental framework of physical laws. which explains the other three basic forces in physics (electromagnetism. Supersymmetric models are constrained by a variety of experiments.II”. including boson mass). supersymmetry could be a component of other theoretical approaches as well. each dimension has If experimental evidence confirms supersymmetry in the its characteristic. These theories can be formulated in three spatial dimensions and one dimension of time. Also. the size of spinors form of supersymmetric particles such as the neutralino is roughly 2d/2 or 2(d − 1)/2 .8 Current status though in theory. and a non-falsifiable theory is generally considered unscientific. Higgs phenomenology and iments.[31] In 2006 these limits were extended by the D0 experiment. rather than a fundamental assumption of the the. and can also provide a natural dark matdirect searches for superpartners (sparticles). the tightest limits were from direct production at colliders. The failure of exSupersymmetry can be reinterpreted in the language of periments to discover either supersymmetric partners or noncommutative geometry and quantum groups. many theoretical physicists continue to focus on supersymmetry because of its usefulness as a tool in quantum field theory. including measurements of low-energy obFor string theory to be consistent.4. This minimum mass can be pushed upwards to arbitrarily large values. be called “loop quantum gravity than four.extra spatial dimensions. known as the quest for a Theory of Everything (TOE). Lee Smolin. string theory. String theory also requires extra spatial Electron–Positron Collider. Since the maximum num. its interesting mathematical properties. any discovered supersymmetry would be consistent with string theory. some ber of supersymmetries is 32. one of the have to be tuned to invoke a particular mechanism to suf- . because its breaking mechanism and the minimum mass above which it is restored are unknown. the anomalous magnetic moment of the muon at Brookhaven. dimensions which have to be compactified as in Kaluza– Klein theory. Since supersymmetry is a required component of eleven. tically between different dimensions.4. at the Large ter candidate.people believe this would be a major boost to string themensions in which a supersymmetric theory can exist is ory. Because the properties of spinors change dras. nor anything else about particle physics. XENON−100. The first mass limits for squarks and gluinos were made at CERN by the UA1 experiment and the UA2 experiment at the Super Proton Synchrotron. although in some LQG theories dimensionality is an emergent property of the theory. LEP later set very strong limits. Historically. quantum gravity researchers. See the main article for more details. supersymmetry appears to be required at some level (although it may be a strongly servables – for example. has encouraged loop ticular. which does not require supersymmetry. namely supercommutativity.that is often believed to be the lightest superpartner. without disproving the symmetry.7 Falsifiability 4. Tevatron and the LHC. In d dimensions.4. and the weak interaction). it involves a mild form of noncommutativity. the strong interaction.4. A significant part of this larger enterprise is the quest for a theory of quantum gravity.4.[32][33] Loop quantum gravity (LQG) predicts no additional spatial dimensions.5 Supersymmetry as a quantum group detect supersymmetric partners or evidence of extra dimensions. In par. supersymmetry is sity measurement and direct detection experiments – for recognized as a way to stabilize the hierarchy between the example. and the possibility that extremely high energy physics (as in around the time of the big bang) are described by supersymmetric theories. In particle theory. many versions of string theory which had preMain article: Supersymmetry as a quantum group dicted certain low mass superpartners to existing particles may need to be significantly revised. al. and by particle collider experunification scale and the electroweak scale (or the Higgs B-physics. However. LQG is a theory of quantum gravity which have strongly constrained supersymmetry models. as of 2013. [39] cluded up to 500 GeV. The resulting fine-tuning of the [35][36][37][38] expected ranges.4. (7) Dirac fermions can be described by a gravIdeas”.. the CMSSM. a As of 2014. THEORY itation theory which includes Cartan torsion (EinsteinCartan theory).“Supersymmetry"--a likely reference to the supersymmeserved neutralinos.[1] Sean Carroll. the LHC has found no evidence for super. should not exceed 130 GeV. and. The preferred masses for squarks and and Tevatron and partially excluded the aforementioned gluinos is about 2 TeV. suggests that the compatible with all present experimenimental limits from the Large Electron–Positron Collider model is still [43] tal constraints.Supersymmetry -rest mass. the NMSSM. Furthermore. This complicates matters because different experiments have looked at dif• Supersymmetric gauge theory ferent sets of points. in the absence of fine tuning (with the supersymmetry breaking scale on the order • Supergeometry of 1 TeV). in 2009.[34] In spite of the null searches and the heavy Higgs.[40] This region of Higgs mass was excluded by LEP by 2000. (5) Neither the ATLAS nor the CMS col. The MSSM predicts that the mass of • Supercharge the lightest Higgs boson should not be much higher than • Superfield the mass of the Z boson. spot is larger than predicted by Lambda cold dark matter models. but not with earlier predictions by supersymmetric [2] Wolchover.. CMSSM squarks have been excluded natural”. with the lightest neutralino and the lightest stau most likely to be found between 100 to 150 GeV. Accessed Oct. Dark Energy: The Dark Side of the Universe. (1) song on their 2013 album Reflektor by the name of The LUX experiment for cold dark matter has not ob.10 In Popular Culture squarks. ".” the Higgs boson are compatible with the standard theory. (8) The mass hierarchy problem of Grand Unified theories need not arise if Grand Unification does not exist. Popular indie rock band Arcade Fire produced a There are eight arguments against supersymmetry. so Grand Unification is not necessary.76 ficiently reduce the neutralino density. CHAPTER 4. The proton decay predicted by Grand Unified theories has not been observed. Neutralinos and sleptons were expected to be quite light. Searches are only applicable for a finite set of tested points because simulation using the Monte Carlo method must be made so that limits for 4. The LHC result is somewhat problematic • Superspace for the minimal supersymmetric model. Guidebook Part laboration have observed gluinos and squarks. though values as high as 2. 7. supersymmetry is not required. is considered “unsummer of 2011. The quantization of electric charge can be explained by theories which include Dirac magnetic monopoles. fits of available data to CMSSM and NUHM1 indicated that squarks and gluinos were most likely to have masses in the 500 to 800 GeV range. the LHC discovered a Higgs boson with a mass of about 125 GeV. Forcing Physics to Seek New models. Some extrapolation between points • Wess–Zumino model can be made within particular models but it is difficult to set general limits even for the Minimal Supersymmetric • Minimal Supersymmetric Standard Model Standard Model. Scientific American. Natalie (November 29. (6) The 2 page 60. 2012). Based on the data sample Higgs boson mass and Z-boson mass (see mu problem collected by the CMS detector at the LHC through the and little hierarchy problem). (4) The number of 4. 2013.. The Teaching Company.9 See also that particular model can be calculated.5 TeV were allowed with low probabilities. • Supersymmetry as a quantum group In 2011 and 2012.11 References faint dwarf galaxies is smaller than predicted by Lambda CDM models.recent analysis of the constrained minimal supersymsymmetry. . (3) The large-scale flow of galaxies is larger than predicted by Lambda CDM models. interaction cross-section and decay rates of A hypothetical symmetry relating bosons to fermions. and with couplings • Quantum group to fermions and bosons which are consistent with the Standard Model. for values of the MSSM parameter tan β ≤ 3. Dark Matter. 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Debevec. ISBN 9783-540-61591-0. Kiesenhofer. Steven. Huang. “Supersymmetry and quantum mechanics”... The Supersymmetric World: The Beginnings of the Theory. Krammer. Bibcode:2004PhRvL. W. Chatrchyan. Kane and Shifman.1016/S0146-6410(02)00177-1. R. . Dragicevic. African Review of Physics 6 (2011) 165-179. PMID 22182023. Duong. New York (2001).. Trotta. • Junker. Hörmann. Press Release.1103/PhysRevLett. Rahbaran. “A Supersymmetry Primer”. Princeton.50. Volume 3: Supersymmetry.107v1804C. Bergauer. Strauss. doi:10.4. Grosse-Perdekamp. arXiv:hep-th/9612114. Sukhatme. Krienen. 2003. Farley. F. M.. “Search for Supersymmetry at the LHC in Events with Jets and Missing Transverse Energy”. Erö.. V.. Iwasaki.107. Carey. A. M. • Joseph D. arXiv:hepex/0401008. Bunce.. Bibcode:2011PhRvL. U.2636 4.095007.. doi:10. D. Lykken (1996).. • Gordon L. A. Rohringer. 2001 Monographs • Weak Scale Supersymmetry by Howard Baer and Xerxes Tata. 2004). Theoretical introductions. • An Introduction to Global Supersymmetry by Philip Arygres. M. Brown..12 Further reading • Supersymmetry and Supergravity page in String Theory Wiki lists more books and reviews. Strege. Druzhinin. W.1007/978-3-642-61194-0. Grossmann. (1992).. Deile. (1999). • “Concise Encyclopedia of Supersymmetry”. Danby.. “Introduction to Supersymmetry”. C.. “Introduction to Supersymmetry”. arXiv:0907.Supersymmetry: Unveiling the Ultimate Laws of Nature Basic Books. THEORY [34] O. G. arXiv:1109. Fabjan. ISBN 0-521-66000-9.. World Scientific. On experiments • Bennett GW.. Khachatryan.3068. G.1103/PhysRevD.7 ppm”. free and online • S. “An Introduction to Supersymmetry”. • Gordon L. Hertzog. (2004).92p1802B. arXiv:1212. Khazin. [42] R. V. Hänsel. • Weinberg. Gray. Singapore (2000).. [41] Patrick Draper et al (December 2011). Hammer.. Bertone. C. [43] “Global Fits of the cMSSM and NUHM including the LHC Higgs discovery and new XENON100 constraints”. 2006. Feroz. Tumasyan. N. M. R. Frühwirth. [39] CMS Collaboration. Hughes. doi:10.. Jungmann.. New g−2 measurement deviates further from Standard Model.. arXiv:hep-ph/9709356. S. doi:10.92.. ISBN 0-7382-0489-7.. (November 2011). J. J. Kronkvist et al. Fornasa. Martin (2011). [35] Implications of Initial LHC Searches for Supersymmetry [36] Fine-tuning implications for complementary dark matter and LHC SUSY searches [37] What LHC tells about SUSY [38] Early SUSY searches at the LHC • Adel Bilal (2001). [40] Marcela Carena and Howard E. ISBN 978-1-40201338-6... J. • Wess. Bibcode:2003PrPNP. Progress in Particle and Nuclear Physics 50: 63. Cushman. Jeitler. Physics Reports 251 (5–6): 267. “Likelihood Functions for Supersymmetric Observables in Frequentist Analyses of the CMSSM and NUHM1”. et al. Haber (1970). Hoch. Ghete. M. Physical Review Letters: 221804. Khare. arXiv:hep-ph/9611409. R. Mikulec. and Jonathan Bagger. T.1016/03701573(94)00080-M. Supersymmetry and Supergravity. I. ISBN 981-024522-X. et al. Fedotovich. Muon (g−2) Collaboration. M. arXiv:hep-th/0101055. doi:10. Taurok. Kawall.221804...78 CHAPTER 4.1103/PhysRevLett. Bibcode:2012PhRvD. PMID 15169217. The Quantum Theory of Fields. Haber. M.. Ruiz de Austri.63C. H. Kane. Hare. eds. 8. doi:10. Kühne: Quantum Field Theory with ElectricMagnetic Duality and Spin-Mass Duality but Without Grand Unification and Supersymmetry. Buchmueller et al. “Supersymmetric Methods in Quantum and Statistical Physics”. Hrubec.. [3] The Higgs boson is named after Peter Higgs. The importance of this fundamental question led to a 40 year search for this elusive particle.13 External links • What do current LHC results (mid-August 2011) imply about supersymmetry? Matt Strassler • ATLAS Experiment Supersymmetry search documents • CMS Experiment Supersymmetry search documents • “Particle wobble shakes up supersymmetry”. proposed the mechanism that suggested the existence of such a particle. such as the reason the weak component separately couples to other particles known force has a much shorter range than the electromagnetic as fermions (via Yukawa couplings). several researchers between about 1960 and 1972 each independently developed different parts of it.scalar field. the discovery of a new “Higgs” terminology particle with a mass between 125 and 127 GeV/c2 was announced. It is also very unstable. the Higgs particle is a boson with no spin. and the construction of one of the world’s most expensive and complex experimental facilities to date. September 2006 • LHC results put supersymmetry theory 'on the spot' BBC news 27/8/2011 • SUSY running out of hiding places BBC news 12/11/2012 79 predicted by the Standard Model.5 Higgs boson components of the Higgs field.[9][10][11] By March 2013. Higgs particles). which in its vacuum state field cannot be “turned off”. including Higgs. 2006). were awarded the Nobel Prize in Physics for their work and prediction.[12] More data is needed to know if the discovered particle exactly matches the predictions of the Standard Model.5. It is a quantum excitation of one of the four 4. Fermilab’s CDF scientists have discovered the quick-change behavior of the B-sub-s meson. • Supersymmetry in optics? “Skulls in the Stars” blog 22/08/2013 In the Standard Model. through its excitations (i.4. Peter Higgs and François Englert. 2013 two of the original researchers. It can be detected if the Higgs boson was not discovered. three components of the this field – now believed to be confirmed – explains why Higgs field are “absorbed” by the SU(2) and U(1) gauge some fundamental particles have mass even though the bosons (the "Higgs mechanism") to become the longitusymmetries controlling their interactions should require dinal components of the now-massive W and Z bosons them to be massless. 4. physicists suspected that it was the Higgs boson. electric charge.[15] Englert’s co-researcher Robert Brout had died in 2011 and the Nobel Prize is not ordinarily given posthumously. HIGGS BOSON • Fermi National Accelerator Laboratory (Sept 25. and also answers several other long. and forms a complex doublet of the weak relevance is that it allows scientists to explore the Higgs isospin SU(2) symmetry. In mainstream media the Higgs boson has often been called the “God particle”.[1] two fundamental attributes of a Higgs boson. but instead takes a non.[13][14] On December 10. The latter constitutes a The Higgs boson or Higgs particle is an elementary par. CERN's Large Hadron Collider. Press Release.4. decaying into other particles almost immediately. This appears to be the first elementary scalar particle discovered in nature. the nickname is strongly disliked by many physicists.[8] able 4. interact and decay in many of the ways . with two neutral and two electrically charged ticle in the Standard Model of particle physics. AlDespite being present everywhere. or whether. the existence of the ternative “Higgsless” models would have been considered Higgs field is very hard to confirm. Some versions of the theory preforce. as predicted by some theories.of the weak force. The remaining electrically neutral standing puzzles in physics. but these are extremely hard to produce and detect. On 4 July 2012. the particle had been proven to behave. causing these to acquire mass as well.e. Its main components.1 A non-technical summary to create Higgs bosons and other particles for observation and study. multiple Higgs bosons exist. one of six physicists who. in 1964. When this happens. or colour charge.breaks the weak isospin symmetry of the electroweak inzero constant value almost everywhere. who regard it as inappropriate sensationalism. and was also tentatively confirmed to have positive parity and zero spin. from a 1993 book on the topic. Although Higgs’s name has come to be associated with this theory. Cosmos magazine. dict more than one kind of Higgs fields and bosons. The field has a "Mexican hat" field[6][7] – a fundamental field first suspected to exist in shaped potential with nonzero strength everywhere (inthe 1960s that unlike the more familiar electromagnetic cluding otherwise empty space). The presence of teraction.5. The variant theory for two of the four fundamental forces had Higgs boson’s importance is largely that it is able to be exconsistently failed at one crucial point: although gauge in.interesting laboratory experiment” with “no useful purery for science and human knowledge. ready brought major developments to society. there are no known immediate technological benin 1962 a new kind of solution that might hold the key. mobile phones and computers.[Note 7] so scientists began to be. efits of finding the Higgs particle. and resistance of macro objects moving through media. motors. at which capable of giving “sensible” results. Evidence of the Higgs field and its properties has been exBut by around 1960 all attempts to create a gauge in. positrons be explored. Although there was point they become the basis for social change and new not yet any evidence of such a field. proof that the Higgs field haywire.tremely significant scientifically.[40][42] anism” almost always means symmetry breaking of the Other observers highlight technological spin-offs from electroweak field. ripples. tently gave answers and predictions that were confirmed by experiments. and the results of massive amounts of data produced by the Large Hadron Collider have already led to significant advances in distributed and cloud computing. as a way to confirm and study the entire Higgs any theory of electromagnetism and the weak force go field theory.both media and science point out that when fundamental searchers. which have aling the exact cause has been difficult. electric fields. can take decades to emerge. other than gravity. By 1972 it had tal discoveries is for practical applications to follow later. medicine.are used in hospital tomography scans.was not expected that quantum mechanics would make lieve this might be true and to search for proof whether possible transistors and microchips. the World Wide Web as used today was created by physicists working in global collaborations on particle experiments at CERN to share their results. for many reasons. like people moving through crowds or some objects moving through syrup or ample. weather prediction. calculations consis. For exVarious analogies have also been invented to describe the Higgs field and boson. which explain black holes also enable have to give off.[43] Radio waves or not a Higgs field exists in nature. were described by their co-discoverer in 1888 as “an If this field did exist. The simplest solution to whether the field ex.In discussion form. mass were massless or that non-existent forces and mass. physicists explain the behaviour of these particles and how they interact us4. However.R. been developed into a comprehensive theory and proved once the discovery has been explored further. It is considered confirmed. but reveal. analogies based on simple resistance to motion are inaccurate as the Higgs field does not work by resisting motion.amined using existing knowledge and experimental techvariance seemed extremely important. that showed the problems could be resolved if discoveries are made about our world. now well established . observers in In 1964 a theory was created by 3 different groups of re. the relevance includes: less particles had to exist. believed to explain almost everything in [18] the world we see. so Electric power generation and transmission. In particle physics. THEORY molasses. in the first half of the 20th century it several other particles. It is imposbroken through a form of the Higgs mechanism. on electricity and magnetism. and is expected to pose” whatsoever. air conditioning and While several symmetries in nature are spontaneously refrigeration resulted from thermodynamics. including analogies with wellknown symmetry breaking effects such as the rainbow and prism. including very accurate predictions of For example. and special and isted was by searching for a new kind of particle it would general relativity. “Real world” impact Work done on superconductivity and “broken” symmetries around 1960 led physicist Philip Anderson to suggest As yet.affect society in the future.this and related particle physics activities.[6][7] Conversely. not.80 Overview CHAPTER 4. by demanding that either many particles with and boson do not exist would also have been significant. television. but are often world-changing It would cause existing particles to acquire mass instead when they do.I. However. scanners. then other more complicated theories would need to wireless computing and emergency response).[43] particle”. it seemed to make nology. known as “Higgs bosons” or the “Higgs satellite-based GPS and satellite navigation (“satnav”). elementary particles and forces give rise to the world around us.2 Significance ing the Standard Model—a widely accepted and “remark[17] ably” accurate framework based on gauge invariance Scientific impact and symmetries.5. this would be a monumental discov.technologies.[40][41][42] A common pattern for fundamenof new massless particles being formed. lasers and M. These would be extremely difficult to find. Scientists had no idea how to get past this point.[44] and are now used in innumerable open doorways to new knowledge in many disciplines. in the sible to predict how seemingly esoteric knowledge may context of the Standard Model the term “Higgs mech. their practical uses an unusual kind of field existed throughout the universe. Nowadays. and it was only many years later that experimental technology lighting all stemmed from previous theoretical work became sophisticated enough to answer the question. If ways (radar. [Note 10] (Higgs later .[61] which showed that if calculating within the radiation gauge.. HIGGS BOSON 81 within mainstream services. as a byproduct of spontaneous symmetry breaking. attempts to unify known fundamental forces such as the electromagnetic force and the weak nuclear force were known to be incomplete. the Nambu–Goldstone massless mode can combine with the massless gauge field modes to produce a physical massive vector field.. also appeared to rule out many obvious solutions. a subject about which Anderson was (and is) one of the leading experts. but quantum fields and their symmetries.[53] the concept that such a mechanism could offer a possible solution for the “mass problem” was originally suggested in 1962 by Philip Anderson (who had previously written papers on broken symmetry and its outcomes in superconductivity[54] and concluded in his 1963 paper on Yang-Mills theory that “considering the superconducting analog. by three groups of physicists: by François Englert and Robert Brout in August 1964.[51][52] The mathematical theory behind spontaneous symmetry breaking was initially conceived and published within particle physics by Yoichiro Nambu in 1960.[45][46] understood. independently and almost simultaneously. the phenomenon of confinement realized in QCD. By the very early sixties.. At the beginning of the 1960s a number of these particles had been discovered or proposed.[55]:4–5[56] and Abraham Klein and Benjamin Lee showed in March 1964 that Goldstone’s theorem could be avoided this way in at least some non-relativistic cases and speculated it might be possible in truly relativistic cases. Carl Hagen.” theory it has massless particles which don’t Hawking however clarified that the only way to accelerate correspond to anything we see. including non-abelian models such as Yang–Mills theory (1954).[57] These approaches were quickly developed into a full relativistic model.4. some of which had already been reformulated as field theories in which the objects of study are not particles and forces. This could mean that the universe marised the state of research at the time: could undergo catastrophic vacuum decay.[49] since it appeared to show that zero-mass particles would have to also exist that were The Higgs mechanism is a process by which vector bosons can get rest mass without explicitly breaking gauge invariance.[48] Goldstone’s theorem. This theory had one huge problem: in perturbation could happen at any time and we wouldn't see it coming.acting as force carriers. with a bubble “Yang and Mills work on non-abelian gauge of the true vacuum expanding at the speed of light. One way of particles above 100bn gigaelectronvolts was with a partigetting rid of this problem is now fairly wellcle accelerator larger than planet Earth.gauge bosons . when you have both gauge symmetry and spontaneous symmetry breaking. leaving finite mass bosons”). What Philip Anderson realized and worked out in the summer of 1962 was that..” [text condensed] [48] Nobel Prize Laureate Peter Higgs in Stockholm.[50] According to Guralnik. along with theories suggesting how they relate to each other. Goldstone’s theorem and Gilbert’s objection would become inapplicable. people had See also: 1964 PRL symmetry breaking papers and Higgs begun to understand another source of massmechanism less particles: spontaneous symmetry breaking Particle physicists study matter made from fundamental of a continuous symmetry. physicists how these problems could be Stephen Hawking in the preface of his book Starmus had “no understanding” [50] overcome. This is what happens in superconductivity.[58] by Peter Higgs in October 1964. which held great promise for unified theories. One known omission was that gauge invariant approaches. also seemed to predict known massive particles as massless.5. relating to continuous symmetries within some theories.[59] and by Gerald Guralnik. where the strong interactions 4.[41] “simply not seen”. wrote. December 2013 particles whose interactions are mediated by exchange particles .[60] Higgs also wrote a short but important[51] response published in September 1964 to an objection by Gilbert.5. “The Higgs potential has the worrisome feature that it might become metastable at energies above 100bn Particle physicist and mathematician Peter Woit sumgigaelectronvolts. and Tom Kibble (GHK) in November 1964.[47]:150 However. [t]hese two types of bosons seem capable of canceling each other out.3 History get rid of the massless “gluon” states at long distances. 166. Coleman found in a study that “essentially no-one ralnik states that in the GHK model the boson is mass[74] paid any attention” to Weinberg’s paper prior to 1971 – now the most cited in particle physics[75] – and even less only in a lowest-order approximation. A 1974 paper and comprehensive review in Reviews of Mod. and adds that the GHK paper was the only one Salam’s.[Note 7] Many of those involved eventually 4. Guample.[65] and further by GHK in 1967. Weinberg was the first to observe that this would also provide mass terms for the fermions.decay and the decays can prove the mechanism.[64] by Kibble in 1967.[59][60] Higgs’ subsequent 1966 paper showed the gauge symmetries were at first largely ignored.36(footnote). the Higgs However.[73] In practice. no one quite believed that nature was diabolically clever enough to take advantage of them”. partly due to and again in the 1990s it became possible to write that its success in other areas of fundamental physics such understanding and proving the Higgs sector of the Stan. but it was unknown whether the the. 175 Higgs directly addressed it.was a massive scalar boson was not seen as important. THEORY dard Model was “the central problem today in particle physics”. but it is not in 1970 according to Politzer.the model and to give [50][82] Higgs mechanism. who combined the work of Veltman clusions.[77][78] Summary and impact of the PRL papers The three papers written in 1964 were each recognised as milestone papers during Physical Review Letters 's 50th anniversary celebration. In reviews dated 2009 and 2011.Gauge invariance is an important property of modern parory was actually correct.including “subof massless vector bosons. vacuum state. Martinus In the paper by Higgs the boson is massive. only a massive boson can it was widely believed that the (non-Abelian gauge) the. despite their very different approaches: Higgs’ and 't Hooft with insights by others. and in a Veltman and Gerard 't Hooft proved renormalisation of closing sentence Higgs writes that “an essential feature” of incomplete multiplets Yang–Mills was possible in two papers covering massless.43–44. Sakurai Prize for Theoretical Particle Physics for this work. three bosons. and popularised the paper essentially used classical techniques. because decay mechanism of the boson. Steven Weinberg[68] and Abdus Salam[69] independently showed how a Higgs mechanism could be used to break the electroweak symmetry of Sheldon Glashow's unified model for the weak and electromagnetic interactions[70] (itself an extension of work by Schwinger).[67] Their six authors were also awarded the 2010 J.[76]:9 adding that the theory Theoretical need for the Higgs had so far produced meaningful answers that accorded with experiment. interest and Brout’s involved calculating vacuum polarization in per[73] acceptance “exploded” and the ideas were quickly abturbation theory around an assumed symmetry-breaking [71][73] sorbed in the mainstream.[62] ) Properties of the model were further considered by Guralnik in 1965. and in particular that they could not be renormalised. or Glashow’s own work. However. Politzer to show that there are no massless Goldstone bosons in a complete analysis of the general states.as electromagnetism and the strong interaction (quantum chromodynamics). the top and charm quarks. forming what became the Standard Model of particle physics. and with great precision. J. ders. All three reached similar concist Benjamin Lee.47 By 1986 ticle theories such as the Standard Model. Glashow’s teaching of the subject to any constraint and acquires mass at higher orweak interaction contained no mention of Weinberg’s. there were great difficulties .[51][52][67] In 1967. In 1971–72. In this way.Main article: Higgs mechanism ern Physics commented that “while no one doubted the [mathematical] correctness of these arguments.4 Theoretical properties won Nobel Prizes or other renowned awards. and the implied existence of [72] stantial” theoretical work by Russian physicists . the seminal papers on spontaneous breaking of boson. but [81]:154. with six being credited for the papers. For ex[60] massive states. ) In the paper even with all key elements of the eventual theory pubby GHK the boson is massless and decoupled from the lished there was still almost no wider interest. of the theory “is the prediction [59] of scalar and vector bosons".[51] neutral currents. Their contribution.[76]:9. only [73] eventually “enormously profound and influential”. and oththat 1960s gauge theorists were focused on the problem ers’ work on the renormalization group . because in the event of a Nobel Prize only up to three scientists could be recognised. (Frank Close comments [71] and then massive. Englert and [73] completed theory. the mass and other properties of some of these.[80] ) Two of the three PRL papers (by Higgs and by GHK) contained equations for the hypothetical field that eventually would become known as the Higgs field and its hypothetical quantum.[63] by Higgs in 1966.82 described Gilbert’s objection as prompting his own paper. ories in question were a dead-end.[71] [Note 11] CHAPTER 4. and GHK used operator formalism and The resulting electroweak theory and Standard Model conservation laws to explore in depth the ways in which have correctly predicted (among other discoveries) weak Goldstone’s theorem may be worked around.5. fields. from 1971. the gauge bosons can consistently acquire a finite mass. almost everyone learned of the theory due to physi.[66] The original three 1964 papers showed that when a gauge theory is combined with an additional field that spontaneously breaks the symmetry.[79] (A controversy also arose the same year. At lower energy levels (right). If Higgs Boson gauge invariance were to be retained.[Note 10] that under certain conditions it might sive W+ . the Standard Model .ing neutral component corresponds to (and is theoretiken without disrupting gauge invariance and without any cally realised as) the massive Higgs boson. thereby producing the expected mass terms.e. Additionally.CP-even.4. but a boson mass term conWeak Gluons Photon tains terms. but particles. W− .the neutral fields are Goldstone bosons. sible for this effect. spin. the simplest known process capable of giving mass to the gauge bosons while remaining compatible with gauge theories.that elementary particles acquire a consistent mass based on how strongly they interact with the Higgs field. the intractable problems of both underlying thethe “Mexican hat” potential comes into effect: “local” symmetry ories “neutralise” each other. two neutral ones and two charged compoA solution to all of these overlapping problems came nent fields. In effect when symmetry breaks under these conditions. based on unsatisfactory properties of the Standard Model.[89] The highest possible mass scale allowed for the Higgs boson (or some other electroweak symmetry breaking mechanism) is 1. The Higgs boson is also its own antiparticle and is [86] The Standard Model hypothesizes a field which is respon. components. and Z bosons. known as in developing gauge theories for the weak nuclear force or the Higgs boson. had to not “break” gauge invariance as the basis for other parts of the theories where it worked well. and had to not require or predict unexpected Properties of the Standard Model Higgs massless particles and long-range forces (seemingly an inevitable consequence of Goldstone’s theorem) which did In the Standard Model. a non-zero vacuum expectation value. which clearly depend on the choice of gauge Bosons and therefore these masses too cannot be gauge invariant. and the residual outcome is inevitably becomes broken since eventually the ball must at ran. these particles their mass. (This can be seen by exe µ τ q amining the Dirac Lagrangian for a fermion in terms of left and right handed components. Below a certain extremely high energy level the existence of this non-zero vacuum expectation spontaneously breaks electroweak gauge symmetry which in turn gives rise to the Higgs mechanism and triggers the acquisition of mass by those particles interacting with the The Minimal Standard Model does not predict the mass of the Higgs boson. we find none of the spin-half particles could ever flip helicity as required for mass. and has zero electric and colour charge. which act as the line case hidden in the mathematics of Goldstone’s longitudinal third-polarization components of the mastheorem. beyond this point. so they must be massless. then the Standard Model can be valid at energy scales all the way up to the Planck scale (1019 GeV).[84] a possible unified electroweak interaction. This effect occurs because scalar field components of the Higgs field are “absorbed” by the massive bosons as degrees of freedom. then these particles had to be acquiring their mass by some other mechanism or interaction..[Note 12] ) W and Z bosons γ g Z W are observed to have mass. It can have this effect because of its unusual “Mexican hat” shaped potential whose lowest “point” is not at its “centre”. which has the unusual property of a non-zero amplitude in its ground state. The quantum of the remaintheoretically be possible for a symmetry to be bro. Both of the charged components and one of from the discovery of a previously unnoticed border.[83] Its quantum would be a scalar boson. the overall “rules” remain symmetrical.[88] Many theorists expect new physics beyond the Standard Model to emerge at the TeV-scale. and the result is symmetrical.4 TeV. and couple to the fermions via Yukawa coupling.5. the Higgs boson has no known as the Higgs mechanism. Therefore it seems that none of the standard model fermions or bosons could “begin” with mass as an inH built property except by abandoning gauge invariance. the Goldstone bosons that arise interact with the Higgs field (and with other particles capable of interacting "Symmetry breaking illustrated": – At high energy levels (left) the with the Higgs field) instead of becoming new massless ball settles in the center. called the Higgs field (symbol: ϕ ). the Higgs field consists of four not actually seem to exist in nature. whatever was giving Summary of interactions between certain particles described by the Standard Model. It is dom roll one way or another.[85] Since the new massless particles or forces. HIGGS BOSON 83 field.[87] If that mass is between 115 and 180 GeV/c2 . and having “sensible” Higgs field is a scalar field (meaning it does not transform (renormalisable) results mathematically: this became under Lorentz transformations). Fermions with a mass term would violate gauge symmetry and thereLeptons Quarks νe νµ τν fore cannot be gauge invariant. i. In practice it is enough to consider the contributions of virtual top and bottom quarks (the heaviest quarks). except for the mass of the Higgs boson itself. then allowing pair. because the LHC collides protons with protons. such as the Fermi constant and masses of W/Z bosons. which emits a Higgs boson. Quantum mechanics predicts that if it is possible for a particle to decay into a set of lighter particles. Most of these factors are fixed by the Standard Model. any absence or difference from theoretical expectations can also be used to improve the theory.g. Precision measurements of electroweak parameters. As of July 2011. Higgs loops result in tiny corrections to masses of W and Z bosons. Since the coupling of particles to the Higgs boson is proportional to their mass.[93][94] nuclei of lead atoms) are used at the LHC. in a particle collider. and it was the second largest contribution for Higgs production at the Tevatron. most notably. If the collided particles are hadrons such as the proton or antiproton—as is the case in the LHC and Tevatron—then it is most likely that two of the gluons binding the hadron together collide. etc. This process is the second most important for the production of Higgs particle at the LHC and LEP. It may still be possible to discover a Higgs boson above these masses if it is accompanied by other particles beyond those predicted by the Standard Model.84 becomes inconsistent without such a mechanism.[93][94][95] • Weak boson fusion. THEORY of the other processes. this process is more likely for heavy particles. then it will eventually do so. which each decay into a heavy quark–antiquark and extremely close to the speed of light. The final process that is commonly conticle can be produced much like other particles that are sidered is by far the least likely (by two orders of studied. The relevant particle theory (in this case the Standard Model) will determine the necessary kinds of collisions and detectors. Higgs Strahlung is also known as associated production. In the Standard Model..[92] Production CHAPTER 4.[93][95] If Higgs particle theories are correct. Protons and lead ions (the bare combine to form a Higgs particle. the desired esoteric particles will occasionally be produced and this can be detected Decay and studied.4 GeV/c2 from the LEP-2 direct search is allowed for[91] ). For a Higgs boson with a mass of . if it carries sufficient energy. where an electron and a positron collided to form a virtual Z boson.[90] It is also possible. making a quark-antiquark collision less likely than at the Tevatron. These indirect constraints rely on the assumption that the Standard Model is correct. At the LHC this process is only the third largest. the strength of the interactions.[93][94][95] although the probability of producing a Higgs boson in any collision is always expected to be very small—for example. because unitarity is violated in certain scattering processes. a quark with an antiquark or an electron with a positron—the two can merge to form a virtual W or Z boson which. This process is the dominant contribution at the LHC and Tevatron being about ten times more likely than any The Standard Model prediction for the decay width of the Higgs particle depends on the value of its mass. Another possibility when two (anti-)fermions collide is that the two exchange a virtual W or Z boson.[93][94] • Higgs Strahlung. the precision electroweak measurements tell us that the mass of the Higgs boson is likely to be less than about 161 GeV/c2 at 95% confidence level (this upper limit would increase to 185 GeV/c2 if the lower bound of 114. can then emit a Higgs boson. only 1 Higgs boson per 10 billion collisions in the Large Hadron Collider. to estimate the mass of the Higgs boson indirectly. for example. an up quark may exchange a Z boson with an anti-down quark. This process was the dominant production mode at the LEP. The easiest way to produce a Higgs particle is if the two gluons combine to form a loop of virtual quarks.[97] This is also true for the Higgs boson. can be used to calculate constraints on the mass of the Higgs. A quark and antiquark from each pair can then them to smash together.[Note 13] The most common expected processes for Higgs boson production are: • Gluon fusion. The colliding fermions do not need to be the same type. In the extreme energies of these collisions. The likelihood with which this happens depends on a variety of factors including: the difference in mass. the Higgs boson has a number of indirect effects. The Standard Model predicts that Higgs bosons could be formed in a number of ways. then a Higgs par• Top fusion. If an elementary fermion collides with an anti-fermion—e. This process involves two colliding glua large number of particles to extremely high energies ons. So. although experimentally difficult. This involves accelerating magnitude). in technicolor the role of the Higgs a mass of 126 GeV/c2 ). Other models. such a decay is only possible if the Higgs is heavier than ~346 GeV/c2 . happens approximately 8. antiquark or into a charged lepton and a neutrino. One way that the Higgs can decay is by splitting into a fermion–antifermion pair. an extended Higgs sector with additional Higgs particle doublets or triplets is also possible.[100] The heavdistinguish from the background.[Note 2] bosons.[99] By this logic the most common decay should be into a top– antitop quark pair. Each of these possible processes has its own probability. gluons or is no Higgs field at all and the electroweak symmetry is photons) is also possible. The SM predicts these branching ratios as a function of the Higgs mass (see plot).5. while the second the Higgs to decay into a pair of W bosons (the light blue doublet does not couple to quarks.[98] The second most common fermion decay at models involves study of the particles’ interactions (“couthat mass is a tau–antitau pair. this process is very relevant for experimental searches for the Higgs boson.ily researched Minimal Supersymmetric Standard Model tons cannot be fully reconstructed (because neutrinos are (MSSM) includes a Type-II 2HDM Higgs sector. the ever. expressed as the branching ratio. and the decays into lep. A could be disproven by evidence of a Type-I 2HDM Higgs. in which the lightest Higgs couples to just for a Higgs boson with a mass of 126 GeV/c2 . but not both. which happens only about pling”) and exact decay processes (“branching ratios”).e. giving an accurate reconstruction of the mass of the decaying particle. the decays of W bosons into quarks are difficult to other only couples to down-type quarks. In the Type-II 2HDM model. However. the fraction of the total number decays that follows that process. which happens only twice for every thousand decays.9% of the time for a Higgs with cle.[98] Much rarer is the decay into a pair of photons mediated by a loop of W bosons or heavy quarks. How.4. For example. For a Higgs mass of 126 GeV/c2 the SM predicts that the most common decay is into a bottom–antibottom quark pair. there Decay into massless gauge bosons (i.techniquarks. In the Type-I 2HDM model one Higgs massive gauge bosons. and many extensions of the Standard Model have this feature. As general rule. (see top quark condensate). and could accommodate a 125 GeV/c2 neutral Higgs boson. 6% of the time.[98] The W fermions (“gauge-phobic") or just gauge bosons (“fermiobosons can subsequently decay either into a quark and an phobic”). a CPodd neutral Higgs boson A0 .one Higgs doublet only couples to up-type quarks. The most likely possibility is for doublet couples to up and down quarks. because the energy and momentum of the photons can be measured very precisely. and two charged Higgs particles H± . which predict the existence of a quintet of scalar particles: two CP-even neutral Higgs bosons h0 and H0 . Supersymmetry (“SUSY”) also predicts relations between the Higgs-boson masses and the masses of the gauge bosons.[99] The Standard Model prediction for the branching ratios of the different decay modes of the Higgs particle depends on the value of its mass. The non-minimal Higgs sector favoured by theory are the two-Higgs-doublet models (2HDM). This model has two inline in the plot). In yet other models.1% of The key method to distinguish between these different the time.5% of the time for a Higgs boson with a mass of 126 GeV/c2 . Alternative models Since it interacts with all the massive elementary particles of the SM.[98] However.[98] which can be measured and tested experimentally in parAnother possibility is for the Higgs to split into a pair of ticle collisions. However.[99] The most common such process is the decay into a pair of gluons through a loop of virtual heavy quarks. feature pairs of top quarks tons (electrons or muons). HIGGS BOSON 85 126 GeV/c2 the SM predicts a mean life time of about of virtual heavy quarks (top or bottom) or massive gauge 1. which happens 56. cleaner signal is given by decay into a pair of Z-bosons In other models the Higgs scalar is a composite parti(which happens about 2. but requires intermediate loop broken using extra dimensions. twice the mass of the top quark. which happens about 23.field is played by strongly bound pairs of fermions called quently decays into a pair of easy-to-detect charged lep.[101][102] . This process. which is the reverse of the gluon fusion process mentioned above. Main article: Alternatives to the Standard Model Higgs The Minimal Standard Model as described above is the simplest known model for the Higgs mechanism with just one Higgs field.. the Higgs boson has many different processes through which it can decay. because the mass of a fermion is proportional to the strength of its interaction with the Higgs. the Higgs is more likely to decay into heavy fermions than light fermions. so it impossible to detect in particle collision experiments).6×10−22 s.1% of the time teresting limits.[98] if each of the bosons subse. the data of hundreds of trillions of collisions needs to be analysed and must “show the same picture” before a conclusion about the existence of the Higgs boson can be reached. it appears that either there is some underlying connection or reason for these observations which is unknown and not described by the Standard Model. . that the observed number of events is more than 5 standard deviations (sigma) different from that expected if there was no new particle. and each known process. and allows physicists to decide whether it is indeed a Higgs boson as described by the Standard Model or some other hypothetical new particle.5. the hierarchy problem amounts to the worry that a future theory of fundamental particles and interactions should not have excessive fine-tunings or unduly delicate cancellations. and should allow masses of particles such as the Higgs boson to be calculable. because Higgs bosons might not be seen in lower-energy experiments.5 Experimental search Main article: Search for the Higgs boson A one-loop Feynman diagram of the first-order correction to the Higgs mass. and it is not clear how to do this. In the Standard Model the effects of these corrections are potentially enormous.[104] More broadly. a powerful particle accelerator was needed. The problem is in some ways unique to spin-0 particles (such as the Higgs boson).[103] A number of solutions have been proposed. a new collider known as the Large Hadron Collider was constructed at CERN with a planned eventual collision energy of 14 TeV—over seven times any previous There are also issues of Quantum triviality. but at the same time the Standard Model requires a mass of the order of 100 to 1000 GeV to ensure unitarity (in this case. Further theoretical issues and hierarchy problem Main articles: Hierarchy problem and Hierarchy problem § The Higgs mass The Standard Model leaves the mass of the Higgs boson as a parameter to be measured. This is seen as theoretically unsatisfactory. which can give rise to issues related to quantum corrections that do not affect particles with spin. comprising over 170 computing facilities in a worldwide cles. although rarely. if the detector detects more decay signatures consistently matching a Higgs boson than would otherwise be expected if Higgs bosons did not exist. So.Grid. To conclude that a new particle has been found.collider—and over 300 trillion (3×1014 ) LHC proton– gests that it may not be possible to create a consistent proton collisions were analysed by the LHC Computing quantum field theory involving elementary scalar parti. To find the Higgs boson.. the Standard Model precisely predicts the likelihood of each of these. This is known as a hierarchy problem. More collision data allows better confirmation of the physical properties of any new particle observed. Because the weak force is about 1032 times stronger than gravity.[103] Reconciling these points appears to require explaining why there is an almost-perfect cancellation resulting in the visible mass of ~ 125 GeV.86 CHAPTER 4. If the observed decay products match a possible decay process (known as a decay channel) of a Higgs boson. To produce Higgs bosons.[105] For the announcement of 4 July 2012. THEORY 4. particle detectors cannot detect it directly. including supersymmetry.[Note 13] and many other possible collision events can have similar decay signatures. the world’s largest computing grid (as of 2012). particle physicists require that the statistical analysis of two independent particle detectors each indicate that there is lesser than a one-in-a-million chance that the observed decay signatures are due to just background random Standard Model events—i. Because the Higgs boson decays very quickly. to unitarise longitudinal vector boson scattering). and (linked to this) the Higgs boson’s mass is so much less than the Planck mass or the grand unification energy.e. many processes may produce similar decay signatures. this indicates that a Higgs boson may have been created. Fortunately. conformal solutions and solutions via extra dimensions such as braneworld models. Occasionally. advanced computing facilities were needed to process the vast amount of data (25 petabytes per year as at 2012) produced by the collisions. Finally. In practice. a Higgs boson will be created fleetingly as part of the collision byproducts. then this would be strong evidence that the Higgs boson exists. Instead the detectors register all the decay products (the decay signature) and from the data the decay process is reconstructed. which sug. Because Higgs boson production in a particle collision is likely to be very rare (1 in 10 billion at the LHC). giving rise to the so-called hierarchy problem. two beams of particles are accelerated to very high energies and allowed to collide within a particle detector. occurring. rather than a value to be calculated. or some unexplained and extremely precise fine-tuning of parameters – however at present neither of these explanations is proven. The collider needed to have a high luminosity in order to ensure enough collisions were seen for conclusions to be drawn. particularly as quantum corrections (related to interactions with virtual particles) should apparently cause the Higgs particle to have a mass immensely higher than that observed. [117] It was therefore widely anticipated around the end of 2011.[108] The search continued at Fermilab in the United States. Englert.[133] The two teams had been working 'blinded' from each other from around late 2011 or early 2012.[116] both experiments had seen among their results. but it was the only supercollider that was operational since the Large Hadron Collider (LHC) was still under construction and the planned Superconducting Super Collider had been cancelled in 1993 and never completed. Theory suggested if the Higgs boson existed. the anomalous data at 125 GeV was becoming “too large to ignore” (although still far from conclusive). it was designed to collide two beams of protons. There was no guarantee that the Tevatron would be able to find the Higgs.[129][130] On 4 July 2012 both of the CERN experiments announced they had independently made the same discovery:[131] CMS of a previously unknown boson with mass 125.[125][126] Speculation escalated to a “fevered” pitch when reports emerged that Peter Higgs. ATLAS and CMS. the latest analyses were discussed outside their teams for the first time. In addition. The Tevatron was only able to exclude further ranges for the Higgs mass.[116] meaning they did not discuss their results with each other. confirmed independently by two separate teams and ex- . When additional channels were taken into account. had narrowed down the mass range where the Higgs could exist to around 116-130 GeV (ATLAS) and 115-127 GeV (CMS).6 times that of the Tevatron. the slow emergence of a small yet consistent excess of gamma and 4-lepton decay signatures and several other particle decays. and was shut down on 30 September 2011 because it no longer could keep up with the LHC.4 GeV/c2 .9-sigma. when their 2012 collision data (with slightly higher 8 TeV collision energy) had been examined.[117][118] Discovery of candidate boson at CERN On 22 June 2012 CERN announced an upcoming seminar covering tentative findings for 2012.[114][115] There had also already been a number of promising event excesses that had “evaporated” and proven to be nothing but random fluctuations.[110][111][112] Data collection at the LHC finally commenced in March 2010. and upgradeable to 2 × 7 TeV (14 TeV total) in future. that the LHC would provide sufficient data to either exclude or confirm the finding of a Higgs boson by the end of 2012. the CMS significance was reduced to 4. there was a small (but not significant) excess of events possibly indicating a Higgs boson with a mass between 115 GeV/c2 and 140 GeV/c2 . at an internal meeting of the two team leaders and the director general of CERN. Hagen attending and Kibble confirming his invitation (Brout having died in 2011).[113] By December 2011 the two main particle detectors at the LHC.[105] This level of evidence. was designed specifically to be able to either confirm or exclude the existence of the Higgs boson. its operational readiness was delayed for 14 months by a magnet quench event nine days after its inaugural tests. was to be attending the seminar.less than a one in three-anda-half million chance of error.[134][135] Using the combined analysis of two interaction types (known as 'channels’). and the team leaders at both ATLAS and CMS each privately suspected they might have found the Higgs. 2011.6 GeV/c2 . and initial preparations commenced in case of a successful finding.[105][106][107] Search prior to 4 July 2012 The first extensive search for the Higgs boson was conducted at the Large Electron–Positron Collider (LEP) at CERN in the 1990s.6 GeV/c2[132][133] and ATLAS of a boson with mass 126. who proposed the particle.[109] The Large Hadron Collider at CERN in Switzerland. However from around May 2011. where the Tevatron—the collider that discovered the top quark in 1995—had been upgraded for this purpose.[116] On November 28.3 ± 0. At the end of its service in 2000.[122][123] and shortly afterwards (from around 1 July 2012 according to an analysis of the spreading rumour in social media[124] ) rumours began to spread in the media that this would include a major announcement. Guralnik.[Note 14] This implied that if the Higgs boson were to exist it would have to be heavier than 114. the narrowing of the possible Higgs range to around 115–130 GeV and the repeated observation of small but consistent event excesses across multiple channels at both ATLAS and CMS in the 124-126 GeV region (described as “tantalising hints” of around 2-3 sigma) were public knowledge with “a lot of interest”. but it was unclear whether this would be a stronger signal or a formal discovery. caused by a faulty electrical connection that damaged over 50 superconducting magnets and contaminated the vacuum system.0 ± 0. or almost 3.[116] While this information was not known publicly at the time.[116] By around Novem- 87 ber 2011. The final analysis of the data excluded the possibility of a Higgs boson with a mass between 147 GeV/c2 and 180 GeV/c2 .5 TeV per beam (7 TeV total). collisions at these energy levels should be able to reveal it.4. LEP had found no conclusive evidence for the Higgs.5. suggesting both ATLAS and CMS might be converging on a possible shared result at 125 GeV. providing additional certainty that any common finding was genuine validation of a particle. Built in a 27 km tunnel under the ground near Geneva originally inhabited by LEP. As one of the most complicated scientific instruments ever built. all hinting at a new particle at a mass around 125 GeV. initially at energies of 3.[127][128] and that “five leading physicists” had been invited – generally believed to signify the five living 1964 authors – with Higgs. both experiments independently reached a local significance of 5-sigma —. HIGGS BOSON network across 36 countries. In early March 2013.4 (stat) ± 0.4. it could still have been a Higgs boson or some other announce a confirmed discovery.[99] To allow more opportunity for data collection. On one hand. absence of “sig.9-sigma (1 in 588 million chance of late 2012. the experimencurrent status tal uncertainties currently still left room for alternative explanations. meets the formal level of proof required to so.88 CHAPTER 4. 7 weeks into 2013. widespread media reports announced (incorbeing due to random background effects) and mass 126.[147] and the deputy chair of physics at Brookhaven National LaboThe new particle tested as a possible Higgs boson ratory stated in February 2013 that a “definitive” an“another few years” after the collider’s Following the 2012 discovery. in a conference in Kyoto researchers ity [two fundamental criteria of a Higgs bosaid evidence gathered since July was falling into line son consistent with the Standard Model]. for example the Brout–Englert–Higgs particle. or the Englert–Brout–Higgs–Guralnik–Hagen– Kibble mechanism. it may take years to Naming be sure.[137][138] Names used by physicists The name most strongly These findings meant that as of January 2013. which improved [140] positively say it was the Higgs boson.6 Public discussion tors noted that based on other particles that are still being understood long after their discovery. the LHC’s proposed “CMS and ATLAS have compared a number 2012 shutdown and 2013–14 upgrade were postponed by [136] of options for the spin-parity of this particle. unknown boson.[138] However some kinds of extensions to the Standard Model would also show very similar results.that do not match a Higgs boson. an answer could be possible 'towards’ mid-2013.[132] In January 2013. so as of December 2012 the new particle was “consisditional data analysis on the “observation of a new parti. that the new particle was some kind of boson. the ATLAS collaboration presented ad. and these all prefer no spin and positive parIn November 2012.[139] so commenta. The behaviours and properties of the particle. the Anderson-Higgs particle.3 ± 0.[Note 15] and these are still used at times. and CMS improved year.5 (sys) GeV/c2 . scientists were very sure they had found an unknown particle of mass ~ 125 GeV/c2 . expected Standard Examples of tests used to validate whether the 125 GeV Model interactions with W and Z bosons. the production rates and branching ratios for the observed channels broadly matched the predictions by the Standard Model within Confirmation of new particle as a Higgs boson. observations remained consistent with 0 was the major remaining requirement to determine the observed particle being the Standard Model Higgs whether the particle is at least some kind of Higgs boson.5. “evap.[137] Physicist Matt Strassler cates that it is a Higgs boson. and scientists did not yet cle”. CERN director-general Rolf-Dieter Heuer stated that based on data analysis to date. and in general no significant deviations to date from the results expected of a Standard Model Higgs boson. with the basic Standard Model more than its alternatives.[51][157] Fueled in part by the issue of recognition . and the particle decayed into at least some of [149] boson. including data from a third channel. coupled with the measured interactions of the with a range of results for several interactions matchnew particle with other particles. This. it was still unconfirmed swer might require [148] 2 2015 restart.particle is a Higgs boson:[138][150] nificant new implications” for or against supersymmetry. Despite this. They were also sure. and the experimental uncertainties. meaning an announcement of the discovery of On 14 March 2013 CERN confirmed that: a Higgs boson would have been premature. also seemed quite close to the behaviours expected of a Higgs boson. However. and decades to fully understand the particle that has been found. in the significance to 5. strongly indiing that theory’s predictions. Moreover. CERN Research whether or not the 125 GeV/c particle was a Higgs boDirector Sergio Bertolucci stated that confirming spinson. from initial observations.0 rectly) that a Higgs boson had been confirmed during the 2 [135] ± 0. the predicted channels. since future tests could show behaviours On 31 July 2012. Even associated with the particle and field is the Higgs boson[81]:168 and Higgs field. so far as examined since July 2012.4 (stat) ± 0.This also makes the particle the first elementary scalar [12] oration” or lack of increased significance for previous particle to be discovered in nature.4 (sys) GeV/c . and had not been misled by experimental error or a chance result. For some time the particle was known by a combination of its PRL author names (including at times Anderson).CERN still only stated that[9][11] tent with” the Higgs boson. THEORY periments.” [1] highlighted “considerable” evidence that the new particle is not a pseudoscalar negative parity particle (consistent with this required finding for a Higgs boson). hints of non-Standard Model findings.[141] the significance to 5-sigma and mass 125. and the An educational collaboration involving an LHC physicist apparent chaos of structures. internally inconsistent.[157][158] the most appropriate name is still occasionally a topic of debate as at 2012..[17] Lederman wrote it in the context of failing US government support for the Superconducting Super Collider... What is the Question[17] p.[181] leaves open numerous questions in fundamental physics. so crucial to our final understanding of the structure of matter. . in an opinion piece in the Institute of Physics' online publication physicsworld. But it is also incomplete and.. or ultimately surmount the challenge and understand “how beautiful is the universe [God has] made”.com. or “the scalar boson”. 22 Lederman whimsically asks whether the Higgs boson was added just to perplex and confound those seeking knowledge of the universe. of sorts. which reduces all of reality to a dozen or so particles and four forces.[168][169][170][171][172] The nickname comes from the title of the 1993 book on the Higgs boson and particle physics . Two main explanations are offered.The God Particle: If the Universe Is the Answer.. What Is the Question? by Nobel Physics prizewinner and Fermilab director Leon Lederman. Nickname The Higgs boson is often referred to as the “God particle” in popular media outside the scientific community. forces and interacand a High School Teachers at CERN educator suggests tions that resulted and shaped our present universe. given its villainous nature and the expense it is causing.and. Why God Particle? Two reasons. and explains that his tongue-in-cheek title Science Sir William Waldegrave[191] and articles in newsdraws an analogy between the impact of the Higgs field papers worldwide. HIGGS BOSON and a potential shared Nobel Prize..[189][190] including coverage of explanatory attempts in their own right and a competition in 1993 Lederman begins with a review of the long human search for the best popular explanation by then-UK Minister for for knowledge.. The God Particle: If the Universe is the Answer.”[187] The name Higgson was suggested as well.. One. —Leon M. to another book.. on the fundamental symmetries at the Big Bang. though that might be a more appropriate title. Lederman and Dick Teresi. Higgs.[173] a part-constructed titanic[174][175] competitor to the Large Hadron Collider with planned collision energies of 2 × 20 TeV that was championed by Lederman since its 1983 inception[173][176][177] and shut down in 1993. and does not explain the ultimate origin of the universe..[181] the particle also has nothing to do with God. was reported to be displeased and stated in a 2008 interview that he found it “embarrassing” because it was “the kind of misuse. with that dispersion of light – responsible for the rainbow and the biblical story of Babel in which the primordial sindispersive prism – is a useful analogy for the Higgs field’s gle language of early Genesis was fragmented into many symmetry breaking and mass-causing effect. it is memorable. yet so elusive. which I think might offend some people”..[157] (Higgs himself prefers to call the particle either by an acronym of all those involved..5.[186] Other proposals A renaming competition by British newspaper The Guardian in 2009 resulted in their science correspondent choosing the name “the champagne bottle boson” as the best submission: “The bottom of a champagne bottle is in the shape of the Higgs potential and is often used as an illustration in physics lectures. particles.[179] many scientists feel the name is inappropriate[13][14][180] since it is sensational hyperbole and misleads readers.[158] ) A considerable amount has been written on how Higgs’ name came to be exclusively used. an atheist. It’s a hard-won Matt Strassler uses electric fields as an analogy:[193] . and whether physicists will be confounded by it as recounted in that story.] remarkably accurate.[184] 89 simplicity [. there is a connection. and [it] has some physics connection too. So it’s not an embarrassingly grandiose name.[188] Media explanations and analogies There has been considerable public discussion of analogies and explanations for the Higgs particle and how the field creates mass. that I have given it a nickname: the God Particle.[185] Today .[192] disparate languages and cultures.[178] While media use of this term may have contributed to wider awareness and interest.. but that (according to Lederman) the publisher rejected all titles mentioning “Higgs” as unimaginative and too unknown.[181][182][183] Science writer Ian Sample stated in his 2010 book on the search that the nickname is “universally hate[d]" by physicists and perhaps the “worst derided” in the history of physics. the publisher wouldn't let us call it the Goddamn Particle..4. we have the standard model. And two. The book sought in part to promote awareness of the significance and need for such a project in the face of its possible loss of funding. This boson is so central to the state of physics today. in fact. a much older one. or “the so-called Higgs particle”. Brout.most cited paper in particle physics. Brout. Those particles that feel the Higgs field act as if they have mass. Higgs. by the ATLAS and CMS experiments at CERN’s Large Hadron Collider The Higgs field’s effect on particles was famously described by physicist David Miller as akin to a room full of political party workers spread evenly throughout a room: the crowd gravitates to and slows down famous people but does not slow down others.90 CHAPTER 4. the theoreticians who derived from these. but can be pers and Weinberg’s 1967 paper A model of Leptons (the somewhat misleading since they may be understood (in. • Nobel Prize in Physics (1979) – Glashow. Salam. Something similar happens in an electric field – charged objects are pulled around and neutral objects can sail through unaffected. The Nobel prize has a limit of 3 persons to share an award. These include a range of theoreticians who made the Higgs mechanism theory possible. or mechanism include: Photograph of light passing through a dispersive prism: the rainbow effect arises because photons are not all affected to the same degree by the dispersive material of the prism.[195] Additionally Physical Review Letters' 50-year review Analogies based on drag effects.[Note 16] He also drew attention [200] to well-known effects in solid state physics where an electron’s effective mass can be much greater than usual in the presence of a crystal lattice. Guralnik. A similar explanation was offered by The Guardian:[194] The Higgs boson is essentially a ripple in a field said to have emerged at the birth of the universe and to span the cosmos to this day . Some particles interact with the Higgs field while others don’t. J.Peter Higgs and François Englert. Englert. or are deceased (the prize is only awarded to persons in their lifetime). for elucidating the quantum structure of electroweak interactions in physics [199] • Nobel Prize in Physics (2008) – Nambu (shared). and which recently was confirmed through the discovery of the predicted fundamental particle. a working electroweak theory and the Standard Model itself. for the theoretical discovery of a mechanism that contributes to our understanding of the origin of mass of subatomic particles. for contributions to the theory of the unified weak and electromagnetic interaction between elementary particles [198] • Nobel Prize in Physics (1999) – 't Hooft and Veltman. and Kibble. as of 2012) “milecorrectly) as saying that the Higgs field simply resists stone Letters”. boson. the evidence required to show the theory is right. Sakurai Prize for Theoretical Particle Physics (2010) – Hagen. for elucidation of the properties of spontaneous symmetry breaking in four-dimensional relativistic gauge theory and of the mechanism for the consistent generation of vector boson masses [79] (for the 1964 papers described above) • Wolf Prize (2004) – Englert.[75] . and the very wide basis of people entitled to consideration. and Weinberg. So you can think of the Higgs search as an attempt to make waves in the Higgs field [create Higgs bosons] to prove it’s really there. made more pointed as a Nobel prize had been expected.. the theoreticians of the 1964 PRL papers (including Higgs himself). THEORY some particles’ motion but not others’ – a simple resistive effect could also conflict with Newton’s third law. and some possible winners are already prize holders for other work. for the discovery of the mechanism of spontaneous broken symmetry in subatomic physics [53] • J. and Higgs • Nobel Prize in Physics (2013) . including analogies of (2008) recognized the 1964 PRL symmetry breaking pa"syrup" or "molasses" are also well known.[197] Recognition and awards There has been considerable discussion of how to allocate the credit if the Higgs boson is proven.. and also the experimentalists at CERN and other institutions who made possible the proof of the Higgs field and boson in reality. The particle is crucial however: it is the smoking gun. Existing prizes for works relating to the Higgs field. [206] If the Higgs potential cannot be measured in this upgraded configuration. strongly constrained by experiments. it cannot be used to claim that one has found the first elementary particle having a 0 spin parameter. some physical parameters were measured at the LHC: its electric charge. is probably the most convicing evidence that the new particle behaves like the Higgs boson should behave. the Higgs boson is the only one to have this 0 spin parameter. since it is also the case of the well-known Z0 boson. When the mass is less than around 200 GeV. and finding a new particle in this mass range is not in itself an evidence that is particle is a Higgs boson. however this is not specific to the Higgs Boson. The lower limit is the result of previous experiments that have excluded that the Higgs boson can have a mass lower than 100 GeV (otherwise one would have already seen it). its parity. The measured parameters at LHC give a partial proof but cannot exclude that this new particle is not the one that explains the mass of the W and Z bosons. • Couplings to other particles. which would clear out any doubt on the identification of this new particle. in which one considers only particles supposed to be elementary.8 Technical aspects and mathematical formulation See also: Standard Model (mathematical formulation) In the Standard Model. The upper limit is a “trick” to avoid a bad consequence of the theoretical model itself. But experimentally speaking. its mass. if confirmed with lower experimental uncertainties. which would support the statement that the particle discovered is actually the Higgs boson. based on the direct observation of decays of the new particle into fermions. This property of the new particle. • Its mass. HIGGS BOSON Following reported observation of the Higgs-like particle in July 2012. this potential cannot be measured at the LHC in its initial configuration. The measured values obtained by both experiments (ATLAS and CMS) are compatible with the theoretic properties of the Higgs boson. but has no physically observable consequence. in June 2014. • Its charge and parity is compatible with the theory but the measured values for these parameters are not specific to the Higgs boson. The missing identification criterion can be to demonstrate the existence of the Higgs potential. By end of 2013 (but published in August 2014). several Indian media outlets reported on the supposed neglect of credit to Indian physicist Satyendra Nath Bose after whose work in the 1920s the class of particles "bosons" is named[201][202] (although physicists have described Bose’s connection to the discovery as tenuous). However there are other well known particles that have a zero spin like the neutral pion or kaon. a collaboration of scientists[204] promoted an alternative explanation to the LHC data based on the Technicolor theory (even though this theory. the Higgs field is a fourcomponent scalar field that forms a complex doublet of the weak isospin SU(2) symmetry: . the CMS collaboration confirmed in a scientific article[205] the identification of the new particle as a Higgs boson. the theoretical problem is still there.4. The newly discovered particle at CERN does interact with both matter particles and gauge bosons.5. against possibly 100 fb−1 expected by end of 2015 for the total integrated luminosity). More specifically: • Its spin. one cannot conclude from the strict application of Gauge Theories (one of them being the “Standard Model”) that the new particle is indeed the one explaining the mass of the W and Z bosons.5. This is why.[207][208] 4. even though a scalar particle. Later. it is never possible to be sure that a particle is elementary or not. In the theory of the standard model. but these particles are not elementary (they are composed of other smaller particles). one must ensure that the field associated to this particle is responsible for the mass of the W and Z bosons. and couplings to other particles (either gauge bosons and matter particles). even if the 0 spin was confirmed. coupling to both matter and gauge bosons is an incredibly good candidate for a Higgs boson. “expected” to be roughly between 100 and 200 GeV. In other words. The statement of this paper seem to rule out alternative models like the Technicolor theory. the core property of the Higgs boson in Peter Higgs seminal article.5. The mass range 91 in which physicists expected to find the Higgs boson is therefore not a constraint given by the theory.[59] Unfortunately. if confirmed to be 0. However. which breaks one of the symmetries on which the Standard Model is based. called the quadratic divergence problem.[203] 4. like the Higgs boson should. The question is then to certify that the new particle is not something mimicking a Higgs boson. corresponds to the theoretical spin of the Higgs boson. The strength of these interactions for the new particle also seem experimentaly to depend on the mass of the involved particles like the theory of the Higgs boson predicts.7 Certification of the new particle as a Higgs boson In order to identify the particle found in 2012 as a Higgs boson. is not the prefered candidate model). but may possibly be measured if the LHC can be upgraded to a higher luminosity in the future (3000 fb−1 required. scientists will then have to wait for the next generation of particle colliders (like the CLIC) to proove the existence of this potential. The Higgs part of the Lagrangian is[209] Standard Model • Quantum gauge theory • Introduction to quantum mechanics • Noncommutative standard model noncommutative geometry generally and where Wµa and Bµ are the gauge bosons of the SU(2) • Standard Model (mathematical formulation) (and and U(1) symmetries. and the weak hypercharge. • Higgs boson in fiction |µ| where v = √ . e. denotes the hermitian conjugate terms.e denote the eigenvalues of the Yukawa matrices. 2 and λ > 0 and µ > 0 . It is always possible to pick a gauge such that in the ground state ϕ1 = ϕ2 = ϕ3 = 0 • Dalitz plot . Quadratic terms in Wµ and Bµ arise.[209] where (d.92 CHAPTER 4. only the terms containing ϕ0 remain. The measured value of this parameλ • Quantum triviality ter is ~246 GeV/c2 . are related by Q = I3 + Y). λij u. γ . which give masses to the W and Z bosons:[209] • Scalar boson • Stueckelberg action 4. Q. one gets where the masses of the fermions are miu. plotted as function of ϕ0 and ϕ3 . In the symmetry breaking ground state.d. [1] Note that such events also occur due to other processes.R are left-handed and right-handed quarks and leptons of the ith generation. .e v/ 2 . and is the only free parameter of the Standard Model that is not a • ZZ diboson dimensionless number. Rotating the quark and lepton fields to the basis where the matrices of Yukawa couplings are diagonal. I3 . THEORY The quarks and the leptons interact with the Higgs field through Yukawa interaction terms: while the field has charge +1/2 under the weak hypercharge U(1) symmetry (in the convention where the electric charge. u. g and g ′ their respective coupling a a a especially Standard Model fields overview and mass constants. Detection involves a statistically significant excess of such events at specific energies. The expectation value of ϕ0 in the ground state (the vacuum expectation value or vev) is then ⟨ϕ0 ⟩ = v . and leave a massless U(1) MZ = 2 ′2 g +g photon.c.5.10 Notes with their ratio determining the Weinberg angle. the weak isospin.[209] 4.9 See also The potential for the Higgs field.5.e = √ λiu. The ground state of Other the Higgs field (the bottom of the potential) is degenerate with different ground states related to each other by a • Bose–Einstein statistics SU(2) gauge transformation.[99] It has units of mass. W √ |g| cos θW = M . so that the ground state breaks the SU(2) symmetry (see figure). and λiu. Y. ν)iL. giving rise to mass terms for the fermions. It has a Mexican-hat or champagne-bottle profile at the ground.d.d.e are matrices of Yukawa couplings where h. τ = σ /2 (where σ are the Pauli matriterms and the Higgs mechanism) ces) a complete set generators of the SU(2) symmetry.d. this looks gϕ0 ψψ exactly like the mass term for a fermion of mass gϕ0 . the gluon. HIGGS BOSON 93 [2] In the Standard Model. This is no catastrophe.21×10−3 GeV.[35][36] [3] The range of a force is inversely proportional to the mass of the particles transmitting it. the more massive a single virtual particle is. so if this happened. and the gauge bosons of the weak force would therefore be expected to be massless. experimental measurement: 91.. would be reconstituted into new fundamental particles and forces and structures. It then became crucial to science. and laws related to conductivity. as can be seen by writing ψ in terms of left and right handed components: ¯ = −m(ψ¯L ψR + ψ¯R ψL ) −mψψ . which means that if we wish to maintain transversality of the photon in all Lorentz frames. temperature. see external links [11] A field with the “Mexican hat” potential V (ϕ) = µ2 ϕ2 + λϕ4 and µ2 < 0 has a minimum not at zero but at some non-zero value ϕ0 . because of underlying quantum fields. A particle’s mass therefore determines the maximum distance at which it can interact with other particles and on any force it mediates. 'unstable' and 'metastable' states (the latter remain stable unless sufficiently perturbed). For example. no better theory yet existed. By the same token.. Newton’s laws of motion apply only at speeds where relativistic effects are negligible. The universe would potentially lose all of its present structures and become inhabited by new ones (depending upon the exact states involved) based upon the same quantum fields. By expressing the action in terms of the field ϕ˜ = ϕ − ϕ0 (where ϕ0 is a constant independent of position). [10] Goldstone’s theorem only applies to gauges having manifest Lorentz covariance. and the Z boson (predicted mass: 91. their masses have since been confirmed by measurement.019 GeV).1876 ± 0. proof breaks down.0021 GeV). The existence of the Z boson was itself another prediction. then the particles and forces we observe in our universe exist as they do. the zero mass Goldstone mesons need not appear. the mass term arising from the ¯ . [4] It is quite common for a law of physics to hold true only if certain assumptions held true or only under certain conditions. And indeed.390 ± 0. and one can readily show that the S-matrix elements.4. this implies that there must exist massive gauge bosons. However space is vast – with even the nearest “the “radiation gauge” condition ∇⋅A(x) = 0 is clearly noncovariant. a condition that took time to become questioned.018 GeV. because the Goldstone et al. and therefore the shorter the distance it can travel. the total decay width of a Higgs boson with a mass of 126 GeV/c2 is predicted to be 4. As a result.[98] The mean lifetime is given by τ = ℏ/Γ . [7] The success of the Higgs based electroweak theory and Standard Model is illustrated by their predictions of the mass of two particles later detected: the W boson (predicted mass: 80.5. experimental measurement: 80. the photon field Aμ(x) cannot transform like a four-vector. gases. [12] In the Standard Model. the reverse is also true: massless and near-massless particles can carry long distance forces. But the process of quantisation requires a gauge to be fixed and at this point it becomes possible to choose a gauge such as the 'radiation' gauge which is not invariant over time. At high energy levels this does not happen. Other correct predictions included the weak neutral current. The world we know depends upon these particles and forces. According to Bernstein (1974. in gauge theories one might arrange things so that one had a symmetry breakdown because of the noninvariance of the vacuum. to know whether it was correct. So the idea that the Standard Model – which relied on a “Higgs field” not yet proved to exist – could be fundamentally incorrect was far from fanciful. so that these problems can be avoided. These particles’ movement and interactions with each other are limited by the energy–time uncertainty principle.8): [5] Electroweak symmetry is broken by the Higgs field in its lowest energy state.. the greater its energy. (See also: Compton wavelength and Static forces and virtual-particle exchange) Since experiments have shown that the weak force acts over only a very short range. everything around us. then existing particles and forces would no longer arise as they presently do. and all fundamental forces. pressure. This Dirac Lagrangian for any fermion ψ is −mψψ is not invariant under the electroweak symmetry. which are observable have covariant structures . Since both g and ϕ0 are constants. including 'stable'. [9] If the Standard Model is correct.1874 ± 0. Quantum fields can have states of differing stability. p. [6] By the 1960s. If a more stable vacuum state were able to arise. The field ϕ˜ is then the Higgs field. many had already started to see gauge theories as failing to explain particle physics because theorists had been unable to solve the mass problem or even explain how gauge theory could provide a solution. so the effect of such an event would be unlikely to arise here for billions of years after first occurring. and classical physics (as opposed to quantum mechanics) may apply only within certain ranges of size. we find the Yukawa term has a component ¯ . and its predictions and solutions were so accurate. and the top and charm quarks. from subatomic particles to galaxies. and others being many billions of lightyears distant. that it became the preferred theory anyway. since the photon field is not an observable. once the entire model was developed around 1972. called its "ground state".[16] In the Standard Model.0021. all later proven to exist as the theory said.387 ± 0. galaxy being over 2 million lightyears from us. [8] The bubble’s effects would be expected to propagate across the universe at the speed of light from wherever it occurred. forces are carried by virtual particles. but. or other conditions. Against this. Different particles or forces would arise from (and be shaped by) whatever new quantum states arose.” [Emphasis in original] Bernstein (1974) contains an accessible and comprehensive background and review of this area. paralleling the interaction for particles that do interact with the field and by doing so. Retrieved 2013-11-03. CERN Bulletin (47–48). Retrieved 2013-10-09.[93] while the total cross-section for a proton–proton collision is 110 millibarn. THEORY i. I would say. But when pressed by journalists afterwards on what exactly 'it' was. Englert. [emphasis in original] [10] Siegfried. because it is so important. 'As a layman.0”. The Guardian. [13] Sample. ProfMattStrassler. the Higgs field is compared to political party workers spread evenly throughout a room. There will be some people (in Miller’s example an anonymous person) who pass through the crowd with ease. [15] Overbye. A. Retrieved 2013-0108. M.. [Q] Why do particle physicists care so much about the Higgs particle? [A] Well. [5] ATLAS collaboration (9 September 2014).5.com. Rev. We see that the mass-generating interaction is achieved by constant flipping of particle chirality. CERN. [9] Biever. CMS-PAS-HIG-14-009.' said Rolf-Dieter Heuer. contributions from ψ¯L ψL and ψ¯R ψR terms do not appear.052004. “The Higgs boson: Why scientists hate that you call it the 'God particle'". Therefore in the absence of some other cause. “Higgs Boson Discovery Confirmed After Physicists Review Large Hadron Collider Data at CERN”. “Particle confirmed as Higgs boson”. Precise determination of the mass of the Higgs boson and studies of the compatibility of its couplings with the standard model (Technical report). J. [6] Onyisi. Retrieved 2009-06-24.] Q: 'are the CERN scientists just being too cautious? What would be enough evidence to call it a Higgs boson?' As there could be many different kinds of Higgs bosons. (29 May 2009). news reports described the finding as a monumental milestone in the history of science. The Wall Street Journal. Higgs. then assuming these gauge charges are conserved in the vacuum. New Scientist. says Vivek Sharma of CMS [. Phys. (14 March 2013). “It’s a boson! But we need to know if it’s the Higgs”. but it was not judged significant enough to extend its run and delay construction of the LHC. [11] Del Rosso. Retrieved 15 September 2014. NBC News. [emphasis in original] [8] Strassler.90. all fermions must be massless.[81] [16] In Miller’s analogy. M. director general of CERN at Wednesday’s seminar announcing the results of the search for the Higgs boson. (8 October 2011).[96] [14] Just before LEP’s shut down. Retrieved 2013-03-14. actually. [2] Bryner. 'We've never seen an elementary particle with spin zero. (8 October 2013). Retrieved 2013-01-08. (14 March 2013).1103/PhysRevD. Hagen. P. Science News. (20 July 2012). (14 March 2013). Retrieved 201301-09. [4] CMS collaboration (2014). none of the spin-half particles could ever swap helicity.com. I. (6 July 2012). the Large Hadron Collider. 'We have discovered a boson – now we have to find out what boson it is’ Q: 'If we don't know the new particle is a Higgs. C. Brout. “New results indicate that new particle is a Higgs boson”. G. [3] Heilprin. Retrieved 2012-12-09. “New Data Boosts Case for Higgs Boson Find”. “The Known Particles – If The Higgs Field Were Zero”. Retrieved 2013-01-09. Retrieved 2013-03-15. University of Texas ATLAS group.e. such as massless photons. In terms usually reserved for athletic achievements. Since the spin-half particles have no right/left helicity pair with the same SU(2) and SU(3) representation and the same weak hypercharge. C. The New York Times. [14] Evans. some events that hinted at a Higgs were observed. the new particle discovered in July is not yet being called the “Higgs boson”. R. things got more complicated. “Anything but the God particle”. Retrieved 13 November 2012.. ProfMattStrassler. [13] The example is based on the production rate at the LHC operating at 7 TeV. The Huffington Post. (14 December 2011). D (American Physical Society) 90 (5): 052004. (14 March 2013). “Higgs Hysteria”. Retrieved 10 July 2014. paralleling the interaction between the field and particles that do not interact with it.11 References [1] O'Luanaigh. The Higgs field: so important it merited an entire experimental facility. CERN. They Can Thank the 'God Particle'". I think we have it. Retrieved 2013-03-14. [12] Naik. D. [15] Other names have included: the “Anderson–Higgs” mechanism. National Post. Kibble and 't Hooft] (by Peter Higgs). “The Higgs FAQ 2. “For Nobel. “Higgs: The beginning of the exploration”. What they really care about is the Higgs field.94 CHAPTER 4. Even in the most specialized circles. (19 November 2012). there’s no straight answer. they don’t. dedicated to understanding it. Retrieved 2013-11-03. “Higgs boson FAQ”. Guralnik. T. J.[195][196] 4.' said Tony Weidberg. doi:10. . what do we know about it?' We know it is some kind of boson. a particle physicist at the University of Oxford who is also involved in the CERN experiments.. acquire a finite mass. (23 October 2012). (12 October 2012). [7] Strassler.[156] “Higgs–Kibble” mechanism (by Abdus Salam)[81] and “ABEGHHK'tH” mechanism [for Anderson. Physicists still hesitate to call it that before they have determined that its properties fit with those the Higgs theory predicts the Higgs boson has. “Measurement of the Higgs boson mass from the H → γγ and H → ZZ* → 4l channels in pp collisions at center-of-mass energies of 7 and 8 TeV with the ATLAS detector”. The total cross-section for producing a Higgs boson at the LHC is about 10 picobarn. There will be other people (in Miller’s example the British prime minister) who would find their progress being continually slowed by the swarm of admirers crowding around. .” Lykken tells us.3305. Frampton (1977). Espinosa. Lederman and Dick Teresi (1993). “The Standard Model Higgs boson as the inflaton”.3568S. A Catastrophic 'Bubble' Could End Universe”.87. [38] Salvio...12.S. University Science Books. “Investigating the nearcriticality of the Higgs boson”. “Why would I care about the Higgs boson?".1378. Degrassi.5. [25] M. doi:10. doi:10. p. doi:10. at a random time and place. The Cern tech that helped track down the God particle. D 87 (5): 53001.072.1016/j. (2000-12-14).2244. Earth will likely be long gone before any Higgs boson particles set off an apocalyptic assault on the universe [33] Hoffman. The good news? It'll probably be tens of billions of years. 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Experiment. Guralnik.1103/PhysRevLett. Anvar (16 July 2012). Bibcode:1964PhL. Chapter 20 • HowStuffWorks: What exactly is the Higgs Boson? 4. Hartosh Singh (19 September 2012). “The Bose in the Boson”. • Collected Articles at the Guardian • Video (04:38) – CERN Announcement on 4 July 2012. Outlook India.122. Bibcode:1964PhRvL. Grober . Interscience Publishers. [198] The Nobel Prize in Physics 1979 – official Nobel Prize website.266. Vol. Hagen and T. at CERN • The Higgs Boson" by the CERN exploratorium.1016/0031-9163(64)91136-9.com “Ask a physicist”. mass media. C. Technicolor Higgs boson in the light of LHC data”. Jona-Lasinio (1961). Bibcode:1961PhRv. In R. Nambu and G.132H. • A. • Carroll. Frandsen. (also: ) • Kibble. Massless Particles and Gauge Fields”. (also: ) . Muhlleitner. doi:10. New York Times Science pages.W. Peter (2010).130. Advances in Physics.R.12 Further reading • G. Nature Physics 10. doi:10.12. AP News.5.. pp. section 7.. Physical Review Letters 12 (10): 266.. “What’s the Matter with the Higgs Boson?". Evidence for the direct decay of the 125 GeV Higgs boson to fermions.B.12.. The measurement of the Higgs self-coupling at the LHC: theoretical status. “Broken Symmetries and Physical Review Letters Massless Particles”. [206] “J.130. [203] Alikhan. [205] “The CMS Collaboration. Retrieved 17 (history)"... documentary film about the search for the Higgs Boson at Fermilab. R. io9. Higgs (1964). and Mads T.102 CHAPTER 4.. Djouadi. THEORY [197] David Goldberg. Retrieved 10 July 2012. “Higgs Boson with Sean Carroll”. Roshan Foadi. Retrieved 22 July 2013.12.5. “The Spark In A Crowded Field”. J.E. [208] “Langacker Paul. • “Particle Fever”.L. Lee (1964). [209] Peskin & Schroeder 1995.713.W. • W.266K.13 External links Popular science. “Dynamical Model of Elementary Particles Based on an Analogy with Superconductivity”. ISBN 978-0470170571.W. Katy (10 July 2012). “Broken Symmetries. [199] The Nobel Prize in Physics 1999 – official Nobel Prize website. page 25 (Summary)". doi:10. [204] “Alexander Belyaev. • P. [202] Bal.1103/PhysRev. New York Times. Brown. Gilbert (1964). • Video1 (07:44) + Video2 (07:44) – Higgs Boson Explained by CERN Physicist. The Standard Model And Beyond..S... Associate Professor of Physics.439A. Bibcode:1963PhRv. Dennis (2013-03-05). Sixty Symbols. 2. Spira (2012). “India: Enough about Higgs. “Does Spontaneous Breakdown of Symmetry Imply ZeroMass Particles?". [201] Daigle. M. Tom (2009).439.713G. London. University of Nottingham. Daniel Whiteson (16 June 2011). 567–708.122. Matthew S.M. .345N. Physical Review 122: 345–358.12. Bibcode:1964PhRvL. 4. Physical Review 130: 439. Retrieved 10 July 2012. ed. Michael J.. • 2001. (p.86 – 88). Liu. arXiv:1110. 14). Sov. SPG MITTEILUNGEN March 2013. Hagen and Kibble development of the Theory of Spontaneous Symmetry Breaking and Gauge Particles”. Bibcode:2009IJMPA. Piled Higher and Deeper. doi:10. Significant papers and other • Observation of a new particle in the search for the Standard Model Higgs Boson with the ATLAS detector at the LHC • Observation of a new Boson at a mass of 125 GeV with the CMS experiment at the LHC • Particle Data Group: Review of searches for Higgs Bosons.. Spontaneous Breakdown of Strong Interaction Symmetry and the Absence of Massless Particles.4. “Heretical Ideas that Provided the Cornerstone for the Standard Model of Particle Physics”. Guralnik. Migdal & A..example of a 1966 Russian paper on the subject. “The Beginnings of Spontaneous Symmetry Breaking in Particle Physics. Gerald (2011).3466. “True Tales from the Road: The Higgs Boson Re-Explained”. containing Higgs’ story of the Higgs Boson.J. .M.91 (1966) . RI. and Guralnik. gauge theories. Jorge (2014-02-19). Proceedings of the DPF-2011 Conference. Providence. Retrieved 2014-02-25.2601G. Introductions to the field • Spontaneous symmetry breaking. (p.1142/S0217751X09045431. No.A. Gerald (2009). USA.an introduction 103 of 47 pages covering the development. and Talk at Brown University about the 1964 PRL papers • Philip Anderson (not one of the PRL authors) on symmetry breaking in superconductivity and its migration into particle physics and the PRL papers • Cartoon about the search • Cham. HIGGS BOSON • Guralnik. the Higgs mechanism and all that (Bernstein. Reviews of Modern Physics Jan 1974) . Duff. history and mathematics of Higgs theories from around 1950 to 1974.-JETP 24. Polyakov. • A.hist-ph].2253v1 [physics. International Journal of Modern Physics A 24 (14): 2601–2627. 8–13 August 2011”. Gerald (2013).24. “The History of the Guralnik.5. 21–25 May 2001. a spacetime odyssey: proceedings of the Inaugural Conference of the Michigan Center for Theoretical Physics : Michigan. ISBN 978-981-238-231-3. arXiv:0907. 39. James T. [1] and these questions were explored in the media.[3] including ultra-high-energy cosmic rays observed to impact Earth with energies far higher than those in any man-made collider.[2] A second review quences.Chapter 5 Safety 5. trigger unforeseen problems or consecollisions pose no conceivable threat.[3][4] It was reviewed and endorsed by a CERN committee of 20 external scientists and by the Executive Committee of the Division of Particles & Fields of the American Physical Society. the LHC particle extreme energy. 5. concerns have view these scenarios.1 Background Main articles: Collider Particle collider and Large Hadron Particle colliders are a type of particle accelerator used by physicists as a research tool to understand fundamental aspects of the universe. The report.[5][6] and was later published in the peer-reviewed Journal of Physics G by the UK Institute of Physics. or whether they might. In a report issued in 2003.[3][7] The report ruled out any doomsday scenario at the LHC. 104 . RHIC and other experiments occur naturally and routinely in the universe without hazardous consequences. which also endorsed its conclusions.Because of the high energy levels involved. CERN mandated a group of independent scientists to re. reaffirmed the safety of the LHC collisions in light of further research conducted since the 2003 assessment. on the Internet and at times through the courts. analysis of the byproducts of these collisions gives scientists good evidence of the structure of the subatomic world and the laws of nature governing it. like current particle experiments such as the lisions are safe. prepared by a group of physicists affiliated to CERN but not involved in the LHC experiments. Their operation involves directed beams of particles accelerated to very high kinetic energy and allowed to collide.arisen at times in the public arena as to whether such colcluded that. The claimed dangers included the production of stable micro black holes and the creation of hypothetical particles called strangelets. impossible to study in other ways. The safety of high energy particle collisions was a topic of widespread discussion and topical interest during the time when the Relativistic Heavy Ion Collider (RHIC) and later the Large Hadron Collider (LHC)—currently the world’s largest and most powerful particle accelerator—were being constructed and commissioned.1 Safety of particle collisions at the Large Hadron Collider of the evidence commissioned by CERN was released in 2008. Concerns arose that such high energy experiments—designed to produce novel particles and forms of matter—had the potential to create harmful states of matter or even doomsday scenarios. around 2008–2010. noting that the physical conditions and collision events which exist in the LHC. by reason of their Relativistic Heavy Ion Collider (RHIC). These may become apparent only at high energies and for tiny periods of time. A simulated particle collision in the LHC. Claims escalated as commissioning of the LHC drew closer.1. and therefore may be hard or To address these concerns in the context of the LHC. they con. ”[27] .2 Relativistic Heavy Ion Collider Main article: Relativistic Heavy Ion Collider Concerns about possible adverse consequences were raised in connection with the RHIC particle accelerator. which began operations in 2008.. the current theoretical picture for particle physics. which set another new world record for the highest energy man-made particle collisions.[8][9] It was built by the European Organization for Nuclear Research (CERN) near Geneva.[10] On 30 March 2010. professor of physics at the University of Oxford.[20] such as creating a black hole.”[13] After detailed studies. heavy-ion experiments at RHIC will not endanger our planet”[26] and that there is “powerful empirical evidence against the possibility of dangerous strangelet production. Concerns were raised in connection with the RHIC particle accelerator.[24] The risk of a doomsday scenario was indicated by Martin Rees. a transition into a different quantum mechanical vacuum (see false vacuum). with Frank Close. both in the media[22][23] and in the popular science media. intended to collide opposing beams of either protons or lead nuclei with very high kinetic energy. the first planned collisions took place between two 3.1.5 TeV beams.g. or the creation of strange matter that is more stable than ordinary matter. with respect to the RHIC. in Switzerland. as being at least a 1 in 50 million chance.”[19] The LHC’s CMS detector. scientists reached such conclusions as “beyond reasonable doubt. The LHC’s main purpose is to explore the validity and limitations of the Standard Model. The first particle collisions at the LHC took place shortly after startup in November 2009. critics postulated that the extremely high energy could produce catastrophic scenarios. professor of physics at the University of Oxford. Frank Close.5. indicates that “the chance of this happening is like you winning the major prize on the lottery 3 weeks in succession. is the world’s largest and highest-energy particle accelerator complex. the problem is that people believe it is possible to win the lottery 3 weeks in succession.[12] and was later postponed for a few weeks until early 2013. nor that tomorrow Earth will be struck with a "doomsday" cosmic ray (they can only calculate an upper limit for the likelihood). scientists reached such conclusions as “beyond reasonable doubt.[11] The LHC will begin to operate at its designed 7 TeV per beam (14 TeV center-of-mass) after a long shutdown that was scheduled to begin at the end of 2012. although obviously not caused by humans. at energies up to 1. RHIC would still modify the chance for the Earth’s survival by an infinitesimal amount. but many predict that the Earth would be destroyed in a time frame from seconds to millennia. without any harm to the Solar System. Physicists are unable to demonstrate experimental and astrophysical constraints of zero probability of catastrophic events.1.[25] With regards to the production of strangelets. Similar concerns had previously also been raised in the context of the Relativistic Heavy Ion Collider. depending on the theory considered.[21] The other main controversial issue was a demand by critics for physicists to reasonably exclude the probability for such a catastrophic scenario. to comment at the time that “the chance of [strangelet creation] is like you winning the major prize on the lottery 3 weeks in succession. the Moon) have been bombarded with cosmic particles of significantly higher energies than that of RHIC and other man made colliders for billions of years. However. heavy-ion experiments at RHIC will not endanger our planet”[18] and that there is “powerful empirical evidence against the possibility of dangerous strangelet production. the problem is that people believe it is possible to win the lottery 3 weeks in succession. the fact that objects of the Solar System (e. Examples of colliders Concerns were noted during the construction of the Large Hadron Collider (LHC). SAFETY OF PARTICLE COLLISIONS AT THE LARGE HADRON COLLIDER 105 5. were among the most striking arguments that these hypotheses were unfounded. According to this argument of upper limits.”[13] Before the Relativistic Heavy Ion Collider started operation. The result would be the same destructive scenarios described above.2 TeV per beam. These hypotheses are complex.[14][15][16][17] After detailed studies. Wagner tried subsequently to stop full energy collision at RHIC by filing Federal lawsuits in San Francisco and New York. “there are more serious things to worry about”[61] and allayed fears that “the atom-smasher might set off earthquakes or other dangerous rumblings”. Marburger.[1][43] Other claimed potential risks include the creation of theoretical particles called strangelets.[29] Institute for Advanced Study. Wagner (an original opponent of the RHIC).[1][43] Based on such safety concerns. “If a black hole is produced under Geneva.[52][53] Media coverage The safety concerns regarding the LHC collisions have attracted widespread media attention.[55] The Guardian. J.[58] and Time.[51] On 9 September 2008. who said that it was “baloney”. SAFETY History of discussion The debate started in 1999 with an exchange of letters in Scientific American between Walter L. The San Francisco suit was dismissed.[57] The Sydney Morning Herald. and the possibility that the qualitative difference between high-E proton collisions with earth or the moon might be different than gold on gold collisions at the RHIC.[39] However. Romania’s Conservative Party held a protest before the European Commission mission to Bucharest. Rees has also reported not to be “losing sleep over the collider. Wilczek.[61] The results of an online survey it conducted “indicate that a lot of [the public] know enough not to panic”. might it swallow Switzerland and continue on a ravenous rampage until the Earth is devoured? It’s a reasonable question with a definite answer: no. English cosmologist and astrophysicist Martin Rees calculated an upper limit of 1 in 50 million for the probability that the Large Hadron Collider will produce a global catastrophe or black hole. RHIC collisions might be described by mathematics relevant to theories of quantum gravity within AdS/CFT. such as the destruction of the Earth.[38][54] Various widely circulated newspapers have reported doomsday fears in connection with the collider.[31] closely followed by articles in the U. in response to a previous article by M.[38][39][40][41][42] These opponents assert that the LHC experiments have the potential to create low velocity micro black holes that could grow in mass or release dangerous radiation leading to doomsday scenarios. I would refer you to the up-to-date safety study. magnetic monopoles and vacuum bub- bles. 1999 by J. Mukerjee.[30] The media attention unfolded with an article in U. 2005. wiping out life.[38] and some scientists associated with the project received protests .”[51] The risk assessments of catastrophic scenarios at the LHC sparked public fears.106 CHAPTER 5.[34] On March 17. it is similar mathematically. the original papers of H. “the scientific consensus appears to be on the side of CERN’s theorists”[62] who say the LHC poses “no conceivable danger”.S. Năstase[36] and the New Scientist article[37] cited by the BBC state that the correspondence of the hot dense QCD matter created in RHIC to a black hole is only in the sense of a correspondence of QCD scattering in Minkowski space and scattering in the AdS 5 × X5 space in AdS/CFT.” and trusts the scientists who have built it. The Daily Mail produced headlines such as “Are we all going to die next Wednesday?"[64] and “End of the world postponed as broken Hadron Collider out of commission until the spring”. “The weather will change completely.[61] The BBC stated. including The Times.[60] MSNBC said that. and attempted to halt the beginning of the experiments through petitions to the US and European Courts.K.[62] Brian Greene in the New York Times reassured readers by saying.[32] The controversy mostly ended with the report of a committee convened by the director of Brookhaven National Laboratory. ostensibly ruling out the catastrophic scenarios depicted. However. but the described physical phenomena are not the same.[33] The New York suit was dismissed on the technicality that the San Francisco suit was the preferred forum. 5.3 Large Hadron Collider Main article: Large Hadron Collider In the run up to the commissioning of the LHC. CNN mentioned that “Some have expressed fears that the project could lead to the Earth’s demise. in other words. Leake. Wagner. media. the BBC published an article[35] implying that researcher Horaţiu Năstase believes black holes have been created at RHIC. US federal judge Richard Posner. There .”[63] The tabloids also covered the safety concerns.[56] The Independent.[65] The Sun quoted Otto Rössler saying. demanding that the experiment be halted because it feared that the LHC could create dangerous black holes. Therefore. Luis Sancho (a Spanish science writer) and Otto Rössler (a German biochemist) expressed concerns over the safety of the LHC.”[60] but it assured its readers with comments from scientists like John Huth. the report left open the possibility that relativistic cosmic ray impact products might behave differently while transiting earth compared to “at rest” RHIC products. Sunday Times of July 18.1.[21] However.[28] and F. but with leave to refile if additional information was developed and presented to the court.[44] Future of Humanity Institute research associate Toby Ord[45] and others[46][47][48][49] have argued that the LHC experiments are too risky to undertake. H. Walter L.the Large Hadron Collider team revealed that they had received death threats and threatening emails and phone calls demanding the experiment be halted. In the book Our Final Century: Will the Human Race Survive the Twenty-first Century?.[59] Among other media sources. but without success.[50] He has stated: “My book has been misquoted in one or two places. [76] holes.a German chemistry professor at the University of Tübingen. As the LHC operates at higher enpossible to create micro black holes at the LHC at a rate ergies than the RHIC or the heavy ion programs of the of the order of one per second. as well as the Earth. argues that micro black holes created in the tivity required to find direct evidence for it. it is far be produced at the LHC.5.] If stable mi“this text would not pass the referee process in a sericroscopic black holes had no electric charge. concludtheir interactions with the Earth would be very ing that “his argument concerns only the General Theweak. while the collisions Hawking radiation allows black holes to lose mass.Concerns not meeting peer review Otto Rössler. [. and to shrink and dissipate instantly. Director of the Albert Einstein Instirays and have stopped in neutron stars and white dwarfs. a remain on Earth. and if they were produced at the LHC.[84] Nicolai concluded that cally charged or neutral.. black in the LHC release energies in the range of 7–14 TeV.[83] and the stability of these astronomical bodies means that Nicolai reviewed Otto Rössler’s research paper on the they cannot be dangerous:[3][77] safety of the LHC[79] and issued a statement highlighting logical inconsistencies and physical misunderstandStable black holes could be either electriings in Rössler’s arguments. Black holes produced in cosmic-ray collisions with bodies such as neutron stars and white dwarf stars would be brought to rest. mod[73] els indicate that strangelets are only stable or long-lived cause they would quickly decay by Hawking radiation. with whom he discussed his safety concerns. ing radiation.. The Daily Strangelets Main article: Strangelets Show’s correspondent John Oliver interviewed Walter L. in Germany. Because ergies (in the range of 1–10 MeV).”[3] LHC could grow exponentially. SAFETY OF PARTICLE COLLISIONS AT THE LARGE HADRON COLLIDER will be a Biblical Armageddon. Rolf Lanproduced by the LHC and were stable. the Committee for Elemenlarger and denser astronomical bodies than the .The probability of the creation of strangelets decreases [3] tence of extra spatial dimensions. some extensions of the Standard Model posit the exis. the LHC is less likely to produce [3] ing to the standard calculations these are harmless be.strangelets than its predecessors. tion to LHC physics.”[85] On 1 August 2008.[71][72][73][74][75] Accord.[78][79][80][81][82] On 4 July According to the LSAG. Those produced by cosmic rays would ory of Relativity (GRT). ous journal.[67] On 10 September 2008. Furthermore.[4] After the dismissal of the federal lawsuit.[3] If strangelets can actually exist. down. The continued existence of such dense bodies.1. The LHC Safety Assessment Group (LSAG) indicates that “there is broad consensus among physicists on the reality of Hawk. Smaller micro black holes (MBHs).[83] unable to accrete matter in a manner dangerous for the Following the meeting. similar Although the Standard Model of particle physics predicts to a strange star. in which it would be at higher energies. However. and makes no logical connecpass harmlessly through the Earth into space. there are much group of German physicists.”[82][84] Domenico Giulini also commented with Hermann Nicolai on Otto Rössler’s thesis. India committed suicide. and strange quarks and that are more stable than ordinary nuclei (strangelets would range in size from a few femtometers to a few meters Specific concerns across). “Success! The world hasn't ended”. the arwhereas those produced by the LHC could gument is not self-consistent. having become distressed about predictions of an impending "doomsday" made on an Indian news channel (Aaj Tak) covering the LHC.[3] that LHC energies are far too low to create black holes.[68] 107 Earth in the Universe.more probable that ice will form spontaneously in boiling [3] ory to be larger net emitters of radiation than larger black water. the argument is not valid. Madhya Pradesh. They would also have been produced by cosmic Hermann Nicolai. Landua asked another expert. are currently predicted by the. Earth. equal numbers of up. to examine Rössler’s arguments. As an example. Rössler met with a CERN physicist. which could than the surrounding medium. tute. since it will either pothetical form of quark matter—that contain roughly [69][70] happen or it won't. who declared that he believed the chance of the Strangelets are small fragments of strange matter—a hyLHC destroying the Earth to be 50%. holes that lose more matter than they gain through other Thermodynamics very strongly disfavors the formation of means are expected to dissipate. but so far no experiment has had the sensi. they could conceivably iniMicro black holes Main article: Micro black hole tiate a runaway fusion process in which all the nuclei in the planet would be converted to strange matter. Hawking radiation is a thermal radiation predicted to be at low temperatures. they would be dua. a 16-year-old girl from Sarangpur. rules out the possibility of the LHC producing any dangerous black holes. Wagner. it had a story entitled.1980s and 1990s. shrink.”[66] After the launch of the collider. and ultimately a cold condensate that is an order of magnitude cooler vanish. even if micro black holes were 2008. Strangelets are bound at low enemitted by black holes due to quantum effects. ruling out the catastrophic growth of black holes in the scenario considered by Plaga. a group of independent scientists. this safety review was published in the Physical Review D. Sergio Fabi and Benjamin Harms posted on the arXiv a paper. as referred to in the LHC safety assessment (LSAG) report. Steven Giddings and Michelangelo Mangano issued a research paper titled the “Astrophysical implications of hypothetical stable TeV-scale black holes”. the LSAG issued a report updating the 2003 safety review.[3] remain robust. One argument raised against doomsday fears was that collisions at energies equivalent to and higher than those of the LHC have been happening in nature for billions of years apparently without hazardous effects.[2] Several of its arguments were based on the predicted evaporation of hypothetical micro black holes by Hawking radiation and on the theoretical predictions of the Standard Model with regard to the outcome of events to be studied in the LHC.[41] On 9 February 2009.[96] The article.[4] On 20 June 2008. relies on a number of new safety arguments as well as certain arguments already present in In 2007.[1][91][92][93] In a follow-up paper posted on the arXiv on 29 August 2008. Peter Braun-Munzinger. a group of external scientists that advises CERN’s governing body.[3][4] The LSAG report was then reviewed by CERN’s Scientific Policy Committee (SPC). SAFETY Safety Assessment Group (LSAG). The report concluded that there is “no basis for any conceivable threat”. the LSAG’s “Review of the safety of LHC collisions” was published in the Journal of Physics G: Nuclear and Particle Physics by the UK Institute of Physics. a German astrophysicist. which summarizes proofs aimed at ruling out any possible black hole disaster at the LHC. performed a safety analysis of the LHC. in which they reaffirmed and extended its conclusions that “LHC collisions present no danger and that there are no reasons for concern”. as ultra-high-energy cosmic rays impact Earth’s atmosphere and other bodies in the universe.[3][7] Following the July 2008 release of the LSAG safety report. the world’s second largest organization of physicists. of the Institute for Nuclear Research in Moscow—to monitor the latest concerns about the LHC collisions.[97] In reaction to the criticisms. a paper titled “Exclusion of black hole disaster scenarios at the LHC” was published in the journal Physics Letters B.[87][88] Otto Rössler was due to meet Swiss president Pascal Couchepin in August 2008 to discuss this concern.[94] On 18 August 2008.[89] but it was later reported that the meeting had been canceled as it was believed Rössler and his fellow opponents would have used the meeting for their own publicity. a group of German quantum physicists. where they develop arguments to exclude any risk of dangerous black hole production at the LHC.108 tary Particle Physics (KET). CERN mandated a group of five particle physi.[86] published an open letter further dismissing Rössler’s concerns and carrying assurances that the LHC is safe.[5][41][98] The report was reviewed and endorsed by a panel of five independent scientists. the LHC Safety Study Group. and released their findings in the 2003 report Study of Potentially Dangerous Events During Heavy-Ion Collisions at the LHC.[95] Giddings and Mangano also referred to the research paper “Exclusion of black hole disaster scenarios at the LHC”.[94] responded to Plaga’s concerns. and Igor Tkachev. and their conclusions were unanimously approved by the full 20 members of the SPC.[90] On 10 August 2008. Michelangelo Mangano and Urs Wiedemann.[94] . Plaga’s paper has not been published in a peer-reviewed journal.[99] and a commentary article which appeared the same day in the journal Physics endorsed Giddings’ and Mangano’s conclusions. of CERN. consisting of John Ellis. in light of new experimental data and theoretical understanding.[1][96] On 19 January 2009 Roberto Casadio.[100] The LSAG report draws heavily on this research. Bryan Webber and Fabio Zwirner. which endorsed its conclusions in a press release that announced the publication.[87][88] Other publications On 20 June 2008.[91] So far. and argued that their own conclusions on the safety of the collider. Matteo Cavalli-Sforza. later published on Physical Review D. the Committee for Elementary Particle Physics (KET).Giddings’ and Mangano’s paper “Astrophysical implicacists not involved in the LHC experiments—the LHC tions of hypothetical stable TeV-scale black holes”.[3] the Executive Committee of the Division of Particles and Fields (DPF) of the American Physical Society. its Council. which relies on a number of new arguments to conclude that there is no risk due to mini black holes at the LHC. the authors of the research paper “Astrophysical implications of hypothetical stable TeV-scale black holes”. posted a research paper on the arXiv Web archive concluding that LHC safety studies have not definitely ruled out the potential catastrophic threat from microscopic black holes. Steven Giddings and Michelangelo Mangano.[86] published an open letter further dismissing concerns about the LHC experiments and carrying assurances that they are safe based on the LSAG safety review. Gian Giudice. issued a statement approving the LSAG’s conclusions and noting that “this report explains why there is nothing to fear from particles created at the LHC”. including the possible danger from Hawking radiation emitted by black holes. Rainer Plaga.[2] CHAPTER 5.[98] On 5 September 2008. Gerard 't Hooft.[6] On 1 August 2008. Plaga updated his paper on the arXiv on 26 September 2008 and again on 9 August 2009. Safety reviews CERN-commissioned reports Drawing from research performed to assess the safety of the RHIC collisions.[95] They pointed out what they see as a basic inconsistency in Plaga’s calculation. (Bundesverfassungsgericht) rejected an injunction peti(Letters to the Editors)". [6] "Statement by the Executive Committee of the DPF on the Safety of Collisions at the Large Hadron Collider" (PDF. that “Given such a state.[115] An appeal against the latter ruling was rejected by the Higher Administrative Court of North Rhine-Westphalia in October 2012.[112] In February 2010 a summary of Johnson’s article appeared as an opinion piece in New Scientist. will inevitably be highly biased in favor of the experiments. Robert (28 August 1999). "Review of the Safety of LHC Collisions" (PDF. CERN. without hearing the case. SPC Report on LSAG Documents.1. CERN record. CERN 2008 (CERN website). [8] CERN Communication Group (January 2008). Johnson states. Giudice G. a complaint requesting an injunction to halt the LHC’s startup was filed by Walter L. [15] Horizon: End Day. Wiedemann U (LHC Safety Assessment Group) (5 September 2008).5. Joel (1 March 2008). [10] CERN press release (2009)" LHC ends 2009 run on a high note. [5] CERN Scientific Policy Committee (2008).1. SAFETY OF PARTICLE COLLISIONS AT THE LARGE HADRON COLLIDER Legal challenges 109 tion to halt the LHC’s operation as unfounded. Wagner and Luis Sancho against CERN and its American collaborators. 176 KiB). In February 2010. Ross GG. Alan (19 August 2008). arXiv:0806. remarkably. 35. [3] Ellis J.[116] On 21 March 2008. it is not clear that any particle-physics testimony should be allowed in the courtroom”. called for summary dismissal of the suit against the government defendants as untimely due to the expiration of a six-year statute of limitations (since funding began by 1999 and has essentially been completed already).3414. 586 KiB).5. "CERN FAQ — LHC: the guide" (PDF). stating that the opponents had failed to produce plausible evidence for their theories. “Black holes at Brookhaven?". . Scientific American 281: 8. New Scientist. was published in the Tennessee Law Review.[104] The LSAG review.[43][101][102] The plain. by reason of this huge personal investment. Study of Potentially Dangerous Events During Heavy-Ion Collisions at the LHC (PDF. a lawyer.[3] The US Government. the German Constitutional Court [16] Wagner.5. PR 48 (08).[109][110][111] In this paper. The Institute of Physics. Geneva (44p). BBC. Cosmic Log. ''Journal of Physics G: Nuclear and Particle Physics. "The God Particle". CERN-2003-001.1088/09543899/35/11/115004.[105] The Hawaii District Court heard the government’s motion to dismiss on 2 September 2008. Madsen J.5 References sessment Group’s (LSAG) most recent safety documentation.[55][59][80] Late in 2009 a review of the legal situation by Eric Johnson.1. Retrieved 2010-03-30. Iliopoulos J. msnbc. 2005. and a permanent injunction until the LHC can [1] Boyle. in reference to the dual problems that (a) the scientific arguments regarding the risks are so complex that only persons who have devoted many years to particle physics study are competent to understand them.[106] A subsequent appeal by the plaintiffs was dismissed by the Court on 24 August 2010. found “no basis for any concerns about the consequences of new particles or forms of matter that could possibly be produced by the LHC”. in response.[80] The suit. National Geographic Magazine. CERN record. [12] CERN Press Office (31 January 2011). 115004 (18pp). which was summarily rejected on the same day. 40 KiB) issued by the Division of Particles & Fields (DPF) of the American Physical Society (APS) [7] "LHC switch-on fears are completely unfounded". Walter (1999). issued on 20 June 2008 after outside review.[103] The US Federal Court scheduled trial to [2] Blaizot JP. and also endangered by severe professional censure if they threaten their continuation.[107][108] On 26 August 2008." [11] “CERN LHC sees high-energy success” (Press release).com. "A Black Hole Ate My Planet". CERN. a group of European citizens. nounces LHC to run in 2012”. before the United States District Court for the District of Hawaii. standards. CERN. "Twists in the Doomsday be demonstrated to be reasonably safe within industry debate". [9] Achenbach. and also called the hazards claimed by the plaintiffs “overly speculative and not credible”. but (b) any such persons. filed a suit against CERN in the European Court of Human Rights in Strasbourg. Tkachev I. Geneva. BBC News.[38] and on 26 September the Court issued an order granting the motion to dismiss on the grounds that it had no jurisdiction over the LHC project. alleged that the Large Hadron Collider posed grave risks for the safety of the 27 member states of the European Union and their citizens. Sonderegbegin 16 June 2009. the National Science Foundation and the Fermi National Accelerator Laboratory.4 See also tiffs demanded an injunction against the LHC’s activation for 4 months after issuance of the LHC Safety As. Specht HJ (2003). doi:10. [4] "The safety of the LHC". 30 March 2010. led by German biochemist Otto Rössler.[113] ger P. the US Department of Energy. “CERN an- [13] BBC End Days (Documentary) [14] Matthews. Mangano ML.[114] A subsequent petition was rejected by the Administrative Court of Cologne in January 2011. 5 September 2008. Cosmic Log. Dar. ABCNEWS.> (2005). [52] "UPDATE: Small Romanian party sparks mockery saying LHC experiment may create tiny black holes and that CERN experiment should be halted". [33] e. "Are accelerators dangerous?" Physics World. [39] "Some fear debut of powerful atom-smasher" CNN. [19] Jaffe. Walter L.72. Physicists Say". 2000. ISBN 0-46506862-6.Com. BBC.com. In 1975. [43] Boyle.L.uk.htm [45] Toby Ord. Sherry R. (1975)). Physical Review Letters.com. "Courts weigh doomsday claims". [41] Overbye. B470: 142–148 (1999) arXiv:hep-ph/9910471 [27] W. 72(4): 1125-140. U. Reviews of Modern Physics. Gerald (10 September 2008). Busza. [38] Boyle. doi:10. Letters to the Editor.umd. Jaffe et al. 18 July 1999. Scientific American 280:March.g. msnbc. Busza. Phys. Phys.bsos. Mod. [50] Overbye. [49] Deatrick. [51] Highfield. SAFETY [34] United States District Court. [46] Bailey. Reich. Wit. The New York Times. Jaffe. 9 . S. Rev. 72. Wagner"". [40] Muir. Roger (5 September 2008). 30 June 2008. Robert L. D. 1125–1140 (2000). Luis (June 2008). Robert (28 August 1999). MIT-CTP-2908. "Review of Speculative “Disaster Scenarios” at RHIC" (PDF). & Heinz. CERN-TH/99-324. [18] Dar. Ronald (2 September 2008). Robert P.co.. "Fear review".. Nastase. Case No. Frank. Alan (2 September 2008). September 2008. 16 (2005). F. Telegraph. Arnon. Anders Sandberg Probing the Improbable: Methodological Challenges for Risks with Low Probabilities and High Stakes (PDF). "Particle smasher 'not a threat to the Earth'". J. [20] T. telegraph.K. p. Journal of System Safety 44: 3.co. 281 no. Eastern District of New York. Hotnews.g. 8. Wagner vs. Wagner. (28 March 2008). for which he subsequently was awarded the Nobel Prize [30] M. Lett. C99-2226. NewScientist. Ulrich (16 December 1999). Rafaela Hillerbrand. "Gauging a Collider’s Odds of Creating a Black Hole".205. De Rújula. "A 1-in-1. Wilzcek.com. Rev. Frank (1999). U.com. Wilczek. doi:10. Issue 2 March 2010. 00CV1672. 9 septembrie 2008. Scientific American July 1999 [25] Cf. [47] Crease. arXiv:0810. 2003. Photonics. arXiv: hep-ph/9910471. "Horizon: End Day". (2008). Department of Energy. 1). et al. “Doomsday Fears at RHIC.1103/RevModPhys. Wagner vs. pages 191 . arXiv:hep-ph/9910333. 470(1): 142-48.com. The Wagner and Wilczek letters follow in the July issue (vol. [42] Sancho. Martin (Lord). June 14. U. Phys. 29 (May 2000) [21] R. Case No. The New York Times. Mod.K.C. Sandweiss. "Doomsday Fears Spark Lawsuit". Harper’s Magazine. U. 60 (1999). Our Final Century: Will the Human Race Survive the Twenty-first Century?. Dennis (21 June 2008). msnbc. R. Hazel. Scientific American 281 (1): 5. L. Northern District of California.. [22] Matthews. De Rujula. 17 March 2005. hep-th/0501068 (2005). Dennis (15 April 2008). (May 2005). [48] Warner. "We must be wary of scientific research". (2000). “Will relativistic heavy ion colliders destroy our planet?". (14 July 2000). MSNBC.S. [23] <Please add first missing authors to populate metadata. "Will relativistic heavy ion colliders destroy our planet?" (PDF). "Earth Will Survive After All. Jack. [37] E. Vol. [32] e. Brookhaven Report mentioned by Rees. [44] Catastrophe: “Risk and Response” http://www. [24] W. Heinz. “A Black Hole Ate My Planet”. [53] "Threats Won't Stop Collider". note that the mentioned “1 in 50 million” chance is disputed as being a misleading and played down probability of the serious risks (Aspden. [36] H. “Large Hadron Collider: Cause for ConCERN or Tempest in a Teapot?". [31] Sunday Times. Volume 13.” Skeptical Inquirer 24. Physical Review D18: 1382–1421 (1978)) [29] Wilczek is noted for his work on quarks. A.110 [17] Wilczek.1125. Alan (27 March 2008). “Black holes at Brookhaven?" and reply by F. from the Internet Archive. “Reply to “Black holes at Brookhaven” by W.L. That claim was later withdrawn in 1978 (“Further Measurements and Reassessment of the Magnetic Monopole Candidate”. he worked on a project that claimed to discover a magnetic monopole in cosmic ray data (“Evidence for the Detection of a Moving Magnetic Monopole”. & Wilczek. New Scientist 185:2491.72:1125–1140 (2000) arXiv:hep-ph/9910333 [28] Wagner is a lawyer and former physics lab technician. Physics Letters B. Alvaro. Mukerjee. Walter L. 2006) [26] A. Reason Magazine. CHAPTER 5.uk. (1999) [35] BBC. "Scientists get death threats over Large Hadron Collider".1016/S0370-2693(99)01307-6. 35.000 Chance of Götterdämmerung: Will European physicists destroy the world?". New Scientist. Cosmic Log. United States District Court. Gutierrez. Sandweiss. “Review of speculative 'disaster scenarios’ at RHIC”. edu/gvpt/lpbr/subpages/reviews/posner505.ro.. Brookhaven Science Associates.5515 Journal of Risk Research. Richard (9 September 2008). [91] Plaga. 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[55] Sugden. doi:10. & Landsberg. 96 KiB). Joanna (6 September 2008). and Nicolai. arXiv:hep-ph/ 0106295v1. "Abraham-Solution to Schwarzschild Metric Implies That CERN Miniblack Holes Pose a Planetary Risk" (PDF.87. Phil (9 September 2008). p.uk. doi:10. "Physicists Allay Fears of the End of the World". [59] Harrell. Taz. 21 KiB). "The Large Hadron Collider: how the press demeans science".96 [70] The Daily Show April 30. CERN Courier. BBC News. 21 July 2008. arXiv:0808.1.com. Daily Mail. Lecture Notes in Physics 769: 387–423. Von Wolf (7 September 2008). "Earth 'not at risk' from collider". [72] Dimopoulos. ISBN 978-3-540-88459-0. "The case for mini black holes". Number 871 #1. Otto (2008). "Big Bang sparks big reaction". Steven B. and Pretorius. [75] Choptuik. 16 KiB). American Institute of Physics. msnbc. promise scientists". Peter (1 August 2008). The Sydney Morning Herald. [81] Patorski. 111101 (2010) [76] Cavaglià. Rainer (10 August 2008). [63] Greene. 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[111] Cartlidge. black holes would instantly evaporate. arXiv:0808. are hypothetical tiny black holes. PhysOrg. 21 March 2008. we can notice that the cosmic rays by US court". physicsworld.1103/PhysRevD. "Memorandum though they reach center of mass energies in the range of on W.2010 PH-TH/2008-184. The lider). 035009 (47 pages).[1] It is possible that such quantum primordial black holes were created in the high-density environment of the early Universe (or big bang).5480J. Rev. trieved 2010-04-01. doi:10.112 CHAPTER 5. also called quantum mechanical black holes or mini black holes. 2010). msnbc. Beside the Harris. Michael (18 August 2008). bombarding the Earth do not produce any damage. Michelangelo L.321. The New York Times. of-the-world scenarios (see Safety of particle collisions Boyle.6 External links • “The safety of the LHC”. Vol. “The Black Hole Case: The In10. Edwin (Feb 2. physletb. alUS Court of Appeals for the 9th Circuit. “The Black Hole Case”. no. & Cho. 5894. NaBibcode:2009arXiv0912. [103] "Documentation submitted by plaintiff".2 Micro black hole Micro black holes. . "Astrophysical implications of hytrieved 2010-04-01. Daniel. Wagner’s Appeal".com (Institute of Physics).5894. (1:2008cv00136)". LHCDe- [104] Boyle. pothetical stable TeV-scale black holes" (PDF. SAFETY [92] Clery. talk by John Ellis at CERN.1016/j. filed on 24 August 2010 hundreds of TeV.2009. Casadio. Re(18 August 2008). Tennessee Law “Large Hadron Collider: Is the LHC a Doomsday MaReview 76: 819–908. 1291. Steven B. or possibly through subsequent phase transitions.com. p. Some hypotheses involving additional space dimensions predict that micro black holes could be formed at an energy as low as the TeV range. Eric E.2. & Mangano.3349. [101] Overbye. Michelangelo L.14. critics say".01. 13 K 5693/08 (in German) Exclusion of black hole disaster scenarios at the LHC (PDF). "Physicists Rule Out the Production of Dangerous Black Holes at the LHC".1126/science. [100] Peskin. Comments on claimed risk from metastable black holes (PDF). "Doomsday Lawsuit at the Large Hadron Collider). Fabi and B.[114] BVerfG. through the particles they are expected to emit by Hawking radiation. doi:10.4087. tional Post. symmetrybreaking. [93] Brean. fense. CERN webpage. arXiv:0912. SLAC/Fermilab. Eric E. p. ence experiment could swallow Earth. 321. CERN 2008. Department of Energy et al. [115] Ruling of the Administrative Court of Cologne. 672 (1): 71–76. Harms Possibility of Catastrophic Black Hole Growth in the Warped Brane-World Scenario at the LHC (PDF). [116] Web portal of the Justice Ministry of North RhineWestphalia (in German). Re[95] Giddings. 78. [99] Mgrdichian. and Maybe a Whole Lot More". PR05. Physics. & Mangano. Cosmic Log. [113] Johnson. 2 BvR 2502/08 vom 18. CERN. However. Laura (1 September 2008). Justia Federal District Court Filings & Dockets.035009. Alan (16 June 2008). doi: [110] Johnson (2009). Steven B. "Doomsday under debate". Alan (26 September 2008).1103/Physics. David (26 August 2010).3381v1. "The end of the world at the Large Hadron Collider?".003. "Government Seeks ticle accelerators such as the LHC (Large Hadron ColDismissal of End-of-World Suit Against Collider". "Is the end nigh? SciL. Case Nr. could a lawsuit shut the LHC down?".com. (29 August 2008). Physical Review D.com. "Asking a Judge to Save the World. Physics Letters B. Stöcker H (9 February 2009). arXiv:0807. American Physical Society. 76 (819): 5480. on 14 August 2008. Bleicher M.1291. [96] Koch B. Popular concerns have then been raised over endNew York Times.1. 1 (14). Dennis (27 June 2008). arXiv:0806. either totally or leaving only a very weakly interacting residue. [105] [106] [107] [108] 5.. such quantum Dismissed". Dennis (29 March 2008). Joseph (9 September 2008). “CERN on trial: CERN-PH-TH/2008-025.. [112] Johnson (2009). msnbc. Cosmic Log. 919 KiB). [109] Johnson. “Law and the end of [94] Giddings.org. Tenn. which are available in parOverbye.S. "LHC lawsuit dismissed theoretical arguments. junction Against the End of the World”.5480. S.874 doi:10. New Scientist. [98] "CERN Council looks forward to LHC start-up". 5.08 (20 June 2008). • “The LHC is safe” (video). chine?" Science. U.78. CERN record [97] R.1. be stable objects. Any primordial black hole of sufficiently low mass will evaporate to near the Planck mass within the lifetime of the Universe. A black hole formed in this way is called a primordial black hole and is the most widely accepted hypothesis for the possible creation of micro black holes. then dark matter. and string total evaporation and production of a Planck-mass-sized theory configurations like the GKP solutions.6×1032 K). With certain special configurations of the extra dimensions. According to the formulae of black hole thermodynamics.2.2 Stability of a micro black hole Main article: Primordial black hole Hawking radiation Main article: Hawking radiation In 1974 Stephen Hawking argued that due to quantum effects. at that time the Universe was not able to collapse into a singularity due to its uniform mass distribution and rapid growth.[7] half the Schwarzschild radius.black hole remnant. This condition gives the Schwarzschild radius. At this stage a black hole would have a Hawking temperature of TP / 8π (5. electrons. where ħ is Reduced planck constant) exceeds While Hawking radiation is sometimes questioned. In this process. In such case.[6] His calculations show that the smaller the size of the black hole. etc. no longer able either to absorb energy graviportant and observable effect at the LHC. this Conjectures for the final state effect can lower the Planck scale to the TeV range.2. time. black hole production could possibly be an im. . these small black holes radiate away matter. It is hypothesized that shortly after the big bang the Universe was dense enough for any given region of space to fit within its own Schwarzschild radius. may in effect by the cosmic rays. however. until it approaches the Planck mass. Computer simulations suggest that the probability of formation of a primordial black hole is inversely proportional to its mass. This smallest mass for a black hole is thus his recent book:[8] “Every so often.[1][2][3][4][5] It tationally like a classical black hole because of the quanwould also be a common natural phenomenon induced tised gaps between their allowed energy levels. the reduced Compton wavelength ( λ = ℏ/M c . the more the black hole loses mass the hotter it becomes.1 Minimum mass of a black hole 113 the other escaping the vicinity of the black hole.black holes. effects will limit the minimum size of a black hole. and M the mass of the black hole. and the faster it evaporates. where h is Planck’s constant. A rough picture of this is that pairs of virtual particles emerge from the vacuum near the event horizon. resulting in a sudden burst of particles as the micro black hole suddenly explodes. gluons.3 Primordial black holes 5. the object can no longer be described as a classical black hole. black holes “evaporate” by a process now referred to as Hawking radiation in which elementary particles (photons.5. In such sce.2. presently unknown. a black hole can have any mass equal to or above the Planck mass (about 22 micrograms). In higher-dimensional space. Thus a thermodynamic description breaks down.[9] other. To make a black hole. Examples of such extensions include large extra dimensions. It is possible that such Planck-mass narios. R = 2GM /c2 . For sufficiently small M. and no black hole descripLeonard Susskind summarizes an expert perspective in tion exists.fringe ideas”.(weakly interacting massive particles). 5. Thus the most likely outcome would be micro black holes. one must concentrate mass or energy sufficiently that the escape velocity from the region in which it is concentrated exceeds the speed of light. the faster the evaporation rate. and Formation in the early Universe Production of a black hole requires concentration of mass or energy within the corresponding Schwarzschild radius. At this point then. they would be WIMPs All this assumes that the theory of general relativity re. Conjectures for the final fate of the black hole include special cases of the Randall–Sundrum model. appear claiming that black holes don't evaporate. MICRO BLACK HOLE 5. a physics paper will approximately the Planck mass. the Compton wavelength. Even so. The net result is the black hole loses mass (due to conservation of energy). represents a limit on the minimum size of the region in which a mass M at rest can be localized.2. Such Some extensions of present physics posit the existence of papers quickly disappear into the infinite junk heap of extra dimensions of space.) are emitted. and Hawking’s calculations also break down. In principle. quarks. does not fully exclude the possibility that black holes of various sizes may have emerged locally. with one member of a pair being captured. this could explain mains valid at these small distances. nor to emit Hawking particles for the same reason. where G is the gravitational constant and c is the speed of light. On the other hand. Such a mini-black hole would also have an entropy of only 4π nats. which means an emitted Hawking particle would have an energy comparable to the mass of the black hole. If it does not. λ = h/M c . the strength of gravity increases more rapidly with decreasing distance than in three dimensions. approximately the minimum possible value. This. to calculate the quantum corrections to ordinary. noncommutative black holes.2. This is far beyond the limits of any current technology.2.2. but Hawking does not provide this calculation or any reference to it to support this assertion. Such quantum black holes should decay emitting sprays of particles that could [1] The Schwarzschild radius of a 1015 gram black hole is be seen by detectors at these facilities. which is much smaller than an Choptuik and Pretorius. It was argued in 2001 that in these circumstances black hole production could be an important and observable effect at the LHC[2][3][4][5][16] 5.7 Notes or future higher-energy colliders. The Large Hadron Collider (LHC) has a design energy of 14 TeV for proton–proton collisions and 1150 • Holeum TeV for Pb–Pb collisions. in some scenarios involving extra dimensions of space. one temporal).[2][3] A paper by ~148 fm (148 x 10−15 m). quantum gravity black holes incorporate quantum gravity effects in the vicinity of the origin.8 References able at the energies of the LHC if additional dimensions are present other than the customary four (three spatial. Giddings. which might be allow. Physical Review Letters. Stephen Hawking also said in chapter 6 of his Brief History of Time that physicist John Archibald Wheeler once calculated that a very powerful hydrogen bomb using all the deuterium in all the water on Earth could also generate such a black hole. where classically a curvature singularity occurs. 2010 in atom but larger than an atomic nucleus.B.[13][14][15][lower-alpha 1] Main article: Safety of high-energy particle collision experiments 5.114 CHAPTER 5. It is estimated that to collide two particles to within a distance of a Planck length with currently achievable magnetic field strengths would require a ring accelerator about 1000 light years in diameter to keep the particles on track. published on March 17. “Quantum black holes”. the Planck mass can be as low as the TeV • Planck particle range. [1] B.Scientific American 292N5 (2005) 30.5 Black holes in quantum theories of gravity It is possible. It has.[17][18] . such black holes would have been produced by cosmic rays and would have already destroyed known astronomical objects such as the Earth. presented a computer-generated proof that micro black holes must form from two colliding particles with sufficient energy. The small radius and high density of the black hole would allow it to pass straight through any object consisting of normal atoms. there are different kinds of quantum gravity black holes. in some theories of quantum gravity. Sun. asymptotically safe black holes. might detect experimental evidence for evaporation of nearby black holes by observing gamma ray bursts.4 Manmade micro black holes Feasibility of production In familiar three-dimensional gravity.J. Carr and S. which would have to be condensed into a region on the order of the Planck length. black holes are singularity free. the minimum energy of a microscopic black hole is 1019 GeV.5. neutron stars. SAFETY Expected observable effects Safety arguments Primordial black holes of initial masses around 1012 Kilograms would be completing their evaporation today.[22][23] 5. Hawking’s calculation[6] and more general quantum mechanical arguments predict that micro black holes evaporate almost instantaneously. however. been suggested that a small black hole (of sufficient mass) passing through the Earth would produce a detectable acoustic or seismic signal. lighter primordial black holes would have already evaporated. or white dwarfs. According to the theory employed to model quantum gravity effects. interacting with only few of its atoms while doing so.[19][20] which showed that in hypothetical scenarios with stable black holes that could damage Earth. 5.[21] and by Fabio Scardigli in 1999 as part of a GUT which could be a quantum gravity candidate. In these approaches.6 See also • Black holes in fiction However. namely loop quantum black holes. Contrarily to conventional black holes which are solutions of gravitational field equations of the general theory of relativity. Virtual-micro black holes (VMBH) have been proposed by Stephen Hawking in 1995. classical black holes.2. launched in June 2008. the Fermi Gamma-ray Space Telescope satellite.2.[1] In optimistic circumstances.[10][11][12] It is unlikely that a collision between a microscopic black hole and an object such as a star or a planet would be noticeable. 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"??".161602. D13 (1976) 198 : first detailed studies of the evaporation mechanism • B. arXiv:hepph/0512112. Phys. L. Phys. [22] Scardigli. Physical Review D 77 (6): 064017. K. Kanti. arXiv:0801. A. Mon. doi:10.. (1975). CERN courier. & Ruban. George (September 11. James (September 26. “Passage of small black hole through the Earth. arXiv:hepph/0106219. Barrau & G.physletb. 4623.104k1101C. G. (2001). Rev. A. Int. Astrophys.. Astrophys. PhysRevD.. “Particle Creation by Black Holes”. 388 (2002) 676. I. A19 (2004) 4899 : evaporating black holes and extra dimensions • D. [18] Peng... [13] Khriplovich. [11] McKee. Matthew W. Rev. Pomeransky. Not. Produit. Frans (2010). November 2004.66. PMID 20366461. & Pretorius.1103/PhysRevD. N. (2000).70. arXiv:hep-th/9904025. Lett. “Satellite could open door on extra dimension”. arXiv:0710. [8] Susskind. Is it detectable?" 0801. (2008). The New York Times. [14] Khriplovich. D 65 (5): 056010. MacGibbon. Phys.. Lett. Page. B 584 (2004) 114 : searches for new physics (quantum gravity) with primordial black holes • P. S.. G.. [9] J.W. Astrophys. [3] Dimopoulos. [16] Schewe.269B. J.633. “The end of the world at the Large Hadron Collider?" Physics 1. [19] S. Lett. “Physicists Strive to Build A Black Hole”. arXiv:hepRev. W. Brown.77. J.199H. Math. S.111101. S. & Thomas.43. 104 (11): 111101. 398 (2003) 403. doi:10. Roy.5.65.2.-y.Park. J. Astroparticle Physics 12 (4): 269–275. Astron.com/+JonathanLangdale/posts/ RUroe4Lv2iu 5. Stephen (1995). ph/0106295. doi:10. Ben & Riordon. to be electrically neutral in their interior.[2] According to this hypothesis. There are at least three ways they might be created in nature: • Cosmogonically. by Norbert Frischauf (also available as Podcast) Size 5. M. and ometry inspired Schwarzschild black hole strange quarks.10 External links more stable than nuclei. The charge screening distance tends to be of the order of a few femtometers. E. down. strangelets are 5.[4] A strangelet is a hypothetical particle consisting of a bound state of roughly equal numbers of up. Fujioka et al. allows more quarks to be placed in lower in Quantum Gravity energy levels. Barrau & J.004: Noncommutative ge.[1] Strangelets have been suggested as a dark The surface tension of strange matter is unknown. Only if many conversions black holes possibly formed at colliders occur almost simultaneously will the number of strange • Mini Black Holes Might Reveal 5th Dimension – quarks reach the critical proportion required to achieve a lower energy state. This stability would occur because of the Pauli exclusion principle. which contains an up. and strange quarks. An equivalent description is that a strangelet is a small fragment of strange matter. • S. Bonanno.3 Strangelet The stability of strangelets depends on their size. But this process may be extremely slow because there is a large energy barrier to overcome: as the TeV-scale black holes weak interaction starts making a nucleus into a strangelet. by decaying via the weak interaction to lighter particles containing only up and down quarks. This is very unlikely to happen. and (b) screening of charges.[2] femtometer[5] ) then large strangelets are unstable and will tend to fission into smaller strangelets (strange stars would 5. SAFETY • P. so Space. According to the strange matter hypothesis.3.11. namely a strangelet. Nature Physics 5. Farhi and R. but requires large strangelets.physletb. so only the outer few femtometers of a strangelet can carry charge. But states with a larger number of quarks might not suffer from this instability. quarks are collected together. PhysRevD. Jaffe.com even if the strange matter hypothesis were correct.. The term “strangelet” originates with E. so if the strange matter hypothesis is correct there should be strangelets in the universe. such as the Lambda particle.2005. 821 – 825 (2009): X-ray astronomy in the laboratory with a Relationship with nuclei miniature compact object produced by laser-driven implosion A nucleus is a collection of a large number of up and down quarks. black lifetime would be longer than the age of the universe. Spallucci.. the lowest energy state is j. and the associated public attention to CERN. dimensions. which are heavy. so strange particles. Smailacic. having • A. Grain. If it is smaller than a critical value (a few MeV per square matter candidate.2. which allows small strangelets to be charged. If it is larger than the critical value.e. such an object is usually called a quark star or “strange star” rather than a strangelet. • A. i.73.2 Natural or artificial occurrence Although nuclei do not decay to strangelets.083005: three types of quarks. This is because of (a) surface tension at the interface between quark matter and vacuum (which affects small strangelets more than big ones).one which has roughly equal numbers of up. down. with a neutralizing cloud of electrons/positrons around them. Reuter.116 CHAPTER 5. such as : a review of the searches for new physics with micro the Lambda. The known particles with strange quarks are unstable because the strange quark is heavier than the up and down quarks.1 Theoretical possibility still be stabilized by gravity). in the early universe when the . and strange quark. when a large enough number of 5. holes. Nicolini.3. like any large piece of matter. confined into triplets (neutrons and protons). rather than two as in normal nuSpacetime Structure of an Evaporating Black Hole clear matter. always lose their strangeness. then strangelets become more stable as they get Strange matter hypothesis bigger. nuclei • Doomsday Machine Large Hadron Collider? – A would never be seen to decay to strangelets because their scientific essay about energies. there are other ways to create strangelets. so nuclei are expected to decay • Astrophysical implications of hypothetical stable into strangelets. The Case for mini black holes the first few strange quarks form strange baryons. Its size would be a minimum of a few femtometers across (with the mass of a light nucleus). A. This is the “strange matter hypothesis” of Bodmer [3] and Witten. Once the size becomes macroscopic (on the order of metres across). down. heavy metorite mass.5. then a larger strangelet would be more stable than a smaller one. an instru. and Earth is reduced to a hot. then occasionally a strangelet should hit Earth. It has been suggested that strangelets of subplanetary • Cosmic ray impacts. and could be able • High energy processes. One speculation that has resulted from the idea is that a strangelet coming into contact with a lump of ordinary matter could convert the ordinary matter to strange matter. Space-based detection 5. that when these collide with each other or with neutron stars they may provide enough energy to overcome the energy barrier and create strangelets from Impacts on Solar System bodies nuclear matter. the conversion scenario System being set up to verify the Comprehensive Nuclear seems much more plausible.duced in heavy-ion colliders has received some media attention. In the end.3. RHIC has been recorded on October 22 and November 24 in 1993. a group of researchers at Southern were comparable to ones which naturally occur as cosmic Methodist University reported the possibility that rays traverse the solar system.2 TJ) energy release or less. would puncture planets and lisions of cosmic rays. straight.[7] but searches are planned[8] for the LHC ALICE detector. all the nuclei of all the atoms of Earth are converted.[21][22][23] It has been suggested that the International Monitoring In the case of a neutron star. creating strange and antistrange quarks which could conceivably lead to strangelet production. and would rarely merge with them. could detect strangelets. STRANGELET 117 QCD confinement phase transition occurred. producing a larger.The danger of catalyzed conversion by strangelets proment which is mounted on the International Space Sta. A neutron star is in a sense Test Ban Treaty (CTBT) after entry into force may be a giant nucleus (20 km across). It is possible properly exploited. These scenarios offer possibilities for observing strangelets. which would cause its trajectory in a magnetic field to be very nearly.[12] strangelets. so we would already have strangelets may have been responsible for seismic events seen such a disaster if it were possible. It is useful as a sort of “strangelet observatory” using the enpossible that strangelets were created along with the tire Earth as its detector. which is predicted by most models to be positively charged. large lump of strange matter. A detailed analysis[14] concluded that the RHIC collisions In May 2002. leading to impact (exit) craters rays impacting on Earth’s atmosphere may create which show characteristic features. after finding that have been raised about the operation of the Large Hadron the clock of one of the seismic stations had a large error Collider (LHC) at CERN[21] but such fears are dismissed during the relevant period. This is not a concern for strangelets in cosmic rays because they are produced far from Earth and have had time to decay to their ground state. held together by gravity. If there are strangelets flying around the universe. The universe is full of very to track strangelets passing through Earth in real time if high-energy particles (cosmic rays). ultra high energy cosmic other solar system objects.e.3 Dangers If the strange matter hypothesis is correct and its surface tension is larger than the aforementioned critical value. more stable strangelet. but not quite. . Similar concerns The authors later retracted their claim. The experimental signature of a strangelet would be its very high ratio of mass to charge. where it would appear as an exotic type of cosmic ray. The Large Hadron Collider (LHC) is even less likely to produce strangelets.[13][14] This "ice-nine"-like disaster scenario is as follows: one strangelet hits a nucleus. catalyzing its immediate conversion to strange matter. nuclei are collided at relativistic speeds.[9] raised[13][20] at the commencement of the Relativistic Heavy Ion Collider (RHIC) experiment at Brookhaven. In addition to head-on coli.[17] The Alpha Magnetic Spectrometer (AMS).[18][19] and concerns of this type were tion. catalyzing its conversion to strange matter.[6] but none were found. Possible seismic detection which could potentially have created strangelets.[10] operating since 2000 without incident. The STAR collaboration has searched for strangelets produced at the RHIC.[15][16] But high-energy collisions could produce negatively charged strangelet states which live long enough to interact with the nuclei of ordinary matter. so they are electrostatically repelled by nuclei.[11] as far-fetched by scientists. If strangelets can be produced in high energy collisions.3. The IMS will be designed to neutrons and protons which form ordinary matter. This liberates energy. which in turn hits another nucleus. detect anomalous seismic disturbances down to 1 kiloton of TNT (4. Accelerator production At heavy ion accelerators like the Relativistic Heavy Ion Collider (RHIC). then we might make them at heavy-ion colliders. “Overview of strangelet searches and Alpha Magnetic Spectrometer: When will we stop searching?" J. Mangano ML. D30. [8] A. “Model of Centauro and strangelet production in heavy ion collisions”. If a strangelet hit a neutron star. but during an early project vert a neutron star to strange matter. D73 114016 (2006) arXiv:hep-ph/0604134 [6] STAR Collaboration. 586 KiB). D4. If any of the objects we call neutron stars could be shown to have a surface made of strange matter. Debate about the strange matter hypothesis The strange matter hypothesis remains unproven. and that region would grow to consume the entire star. Phys. 35. there is an ongoing effort to determine whether the surfaces of neutron stars are made of strange matter or nuclear matter.3. Steiner. Alford. [5] M. • In comic book The Hypernaturals. creating a quark star. the manipulation of strangelets is described as the hypernatural power of Shoal to reinforce mass and find ways out from tight spots. S. published in 2010 and written by Douglas Preston. ''Journal of Physics G: Nuclear and Particle Physics. doi:10. Angelis et al. Giudice G. A. But there is no strong evidence for strange matter surfaces on neutron stars (see below). Forward deals with the making of a strangelet in a particle accelerator. arXiv: nucl-ex/0511047 [7] Ellis J.3414. which would vindicate the strange matter hypothesis. No direct search for strangelets in cosmic rays or particle accelerators has seen a strangelet (see references in earlier sections).3. deals with an alien machine that creates strangelets. 115004 (18pp). a strangelet were true. This argument is still into an additional “sun. Rev. Because of its importance for the strange matter hypothesis. creating a strangelet and starting a catastrophic chain reaction which destroys Earth.[31] [1] E. D48. “Strange Matter”. Because one strangelet will conmostly used as weapons. Heiselberg. Sandweiss.. Atom.6 References would disprove the strange matter hypothesis. • In the 1992 black-comedy novel Humans by Donald E. 5. Rev. 1601 (1971) [4] H. • The story A Matter most Strange in the collection Indistinguishable from Magic by Robert L. Nucl. violent events such • In the novel "The Quantum Thief" by Hannu Raas collisions would soon create many strangelets flying janiemi and the rest of the trilogy. Westlake. Bodmer “Collapsed Nuclei” Phys. published in 2011 and written by Steve Alten as the third and final part of his Domain trilogy.” debated. and otherwise none should be. matter. presents a fictional story where strangelets are unintentionally created at the Large Hadron Collider and escape from it to destroy the Earth. Phys. Rev. Reddy. Phys. “Cosmic Separation Of Phases” Phys. Wiedemann U (LHC Safety Assessment Group) (5 September 2008). K.4 • In The Arwen. D30. This comes from the phenomenology of X-ray bursts. Another argument against the hypothesis is that if it • In the 2010 film Quantum Apocalypse.[25] Even if there were only a few strange stars initially. arXiv:0806.[30] and from measurement of seismic vibrations in magnetars. SAFETY but it is electrically neutral and so does not electrostatically repel strangelets. CERN record. an irritated God sends an angel to Earth to bring about Armageddon by means of using a strangelet created in a particle accelerator to convert the Earth into a quark star. “Strangelet search at RHIC”.[32] • The BBC docudrama End Day features a scenario where a particle accelerator in New York City explodes. Phys. Jaffe. Tkachev I. 272 (1984) [3] A. "Review of the Safety of LHC Collisions" (PDF. by now all neutron to terraform Mars one was used to convert Phobos stars would have been converted. Witten. • Impact. Rev. Farhi and R. Rajagopal. which is well-explained in terms of a nuclear matter crust. 2379 (1984) [2] E. 1418 (1993) 5. it could convert a small region of it. Rev. G30:S51-S59 (2004) .[24] • The novel Phobos. strangelets are used as a method to create a traversable wormhole. “The Stability of Strange Star Crusts and Strangelets”. this would indicate that strange matter is stable at zero pressure.5 In fiction • An episode of Odyssey 5 featured an attempt to destroy the planet by intentionally creating negatively charged strangelets in a particle accelerator.3. all neutron stars should be made of strange approaches the Earth from space.118 CHAPTER 5. 67:396-405 (2004) arXiv:nucl-th/0301003 [9] J.1088/09543899/35/11/115004.[26][27][28][29] but if it is correct then showing that one neutron star has a conventional nuclear matter crust 5. Phys. The machine’s strangelets impact the Earth and Moon and pass through. The evidence currently favors nuclear matter. “Screening in quark droplets”. strangelets are around the universe. T. Dar. Phys. arXiv: nucl-th/9611052 • Fridolin Weber (2004). A. 90:121102 (2003) arXiv: stro-ph/0211597 [27] S. Charles. [“Strange stars” “Strange stars"]. Heinz. Bibcode:2005PrPNP. arXiv:astro-ph/0403515 [11] E.261A. Germany.Phys. 92:119001 (2004).. Phys. B264. NY Times. Phys. Caldwell. “Review of speculative 'disaster scenarios’ at RHIC”. CERN library record CERN Yellow Reports Server (PDF) [24] Alcock. Edward. Balberg. Rev. Diener. 29 March 2008 [22] “Safety at the LHC”. STRANGELET 119 [10] D. “Two seismic events with the properties for the passage of strange quark matter through the earth” arXiv:astro-ph/0205089 [28] J.. A. Greiner. Woosley. for Proceedings of 11th Marcel Grossmann Meeting. ISBN 978-3-540-65209-0.. “Detectability of strange matter in heavy ion experiments”. Lett. Rev. Olinto.310. “The Story of Strangelets”. an episode of the Canadian science fiction television series Odyssey 5 by Manny Coto (2002) 5. Johann Rafelski.Lett.3. doi:10.001. Retrieved 2010-04-01.1016/j. 92:119002 (2004).. F. B470: 142-148 (1999) arXiv:hep-ph/9910471 [14] W. Blaizot et al. [25] J. Wilzcek.3.1195 [31] A. Rutgers. Phys. Watts and S. Rev. Jaffe. Scientific American July 1999 [21] Dennis Overbye. Rev.Notes Phys. Lett. Angela (1986). Galloway. Anderson et al. Jul 2006. Friedman and R.. [23] J. Schaffner-Bielich. “Models of Type I X-ray Bursts from GS 1826-24: A Probe of rp-Process Hydrogen Burning”. MNRAS.. 014026 (2005) arXiv:astro-ph/ 0411538 [12] Lance Labun. an episode of the BBC television series Horizon [20] W.07. arXiv:astroph/9809032.2004. Bibcode:1986ApJ. D. “Strangelet propagation and cosmic ray flux”. |chapter= ignored (help) . Lett. Farhi. “Reply to Comment on Strangelets as Cosmic Rays beyond the Greisen-Zatsepin-Kuzmin Cutoff”. J. Asking a Judge to Save the World. 1998). A. C55:3038-3046 (1997). doi:10.5. De Rujula. “Magnetar oscillations pose challenges for strange stars”. Joshua (May 17. Letters to the Editor. and Maybe a Whole Lot More. Progress in Particle and Nuclear Physics 54: 193–288.. Wagner. Busza.54. Madsen. arXiv:astroph/0407155. S. Lett. “Strangelets as cosmic rays beyond the GZKcutoff”. Reddy. Heger. Madsen. C. Madsen. “Will relativistic heavy ion colliders destroy our planet?". Lect. Madsen “Strangelets in Cosmic Rays”. 85 (2000) 4687-4690 (2000) arXiv:hep-ph/0008217 [30] A.arXiv:1104.7 Further reading [16] J. “Comment on 'strangelets as cosmic rays beyond the Greisen-Zatsepin-Kuzmin cutoff'". Lett. Wilczek. Journal 310: 261. arXiv:astro-ph/0612784 • Holden. Sandweiss. Phys. 28 August 1999: “A Black Hole Ate My Planet” [19] Horizon: End Days. 143-148 (1991) [26] J. “Strange Quark Matter and Compact Stars”. “Black holes at Brookhaven?" and reply by F. L63 (2007) arXiv:astro-ph/0609364 [32] Odyssey 5: Trouble with Harry. Lecture Notes in Physics 516: 162–203. Rev. Phys. U. Phys. “Seismic Search for Strange Quark Nuggets” [29] J.1007/BFb0107314. Mod. Jeremey Birrell. arXiv:0711. H. “Solar System Signatures of Impacts by Compact Ultra Dense Objects”. D71. “Evidence against a strange ground state for baryons”. Astrophys. Phys.193W. Cumming. “Hadrons in Dense Matter and Hadrosynthesis”. [18] New Scientist. Madsen. “Intermediate mass strangelets are positively charged”. [17] J. Herrin et al. arXiv:astro-ph/0403503 • Jes Madsen (1998). Rev. 379. “Study of Potentially Dangerous Events During Heavy-Ion Collisions at the LHC”. Rev.ppnp.. Stoecker.4572 [13] A. doi:10.1086/164679.72:1125-1140 (2000) arXiv:hep-ph/9910333 [15] J. R. at the latest LUMI'06 workshop. The upgrade aims at increasing the luminosity of the machine by a fac.1.[3] ATLAS upgrade web page tor of 10. up to 1035 cm−2 s−1 . However. The Very Large Hadron Collider (VLHC) is a hypothetical future hadron collider with performance significantly beyond the Large Hadron Collider.2 References The High Luminosity Large Hadron Collider (HL. The maximum integrated luminosity increase of the existing options is about a factor of 4 higher than the LHC ultimate performance. Not to be confused with Very Large Hadron Collider. or significant increase in bunch length and population. 6.3 External links measurements. 6.[2] several suggestions were proposed that would boost the LHC peak luminosity by a factor of 10 beyond nominal towards 1035 cm−2 s−1 . Proton Synchrotron 2 (PS2): Accelerating the beam from 5 GeV at injection to 50 GeV at extraction. Many different paths exist for upgrading the collider.Chapter 6 Future 6. • A comprehensive press article on the 2006 workshop can be found at the CERN Courier. A collection of different designs of the high luminosity interaction regions is being maintained by the European Organization for Nuclear Research (CERN). providing a better chance to see rare processes and improving statistically marginal 6.[3] There is no planned location or schedule for the VLHC. Super Large Hadron Collider) is a proposed upgrade to the Large Hadron Collider to be [2] LUMI 06 workshop made after around ten years of operation. 6. unfortunately far below the LHC upgrade project’s initial ambition of a factor of 10. the name is used only to discuss the technological feasibility of such a collider and ways that it might be designed.1 Injector upgrade Given that such a performance increase necessitates a correspondingly large increase in size. 6.1.1. formerly SLHC.2.[2] Increasing LHC luminosity involves reduction of beam size at the collision point and either reduction of bunch length and spacing. ration over a period of decades would be required to con[1] Superconducting Proton Linac (SPL): Accelerating struct such a collider. protons with superconducting radio frequency cavities to an energy of 5 GeV.2 Very Large Hadron Collider Not to be confused with Large Hadron Collider or Super Large Hadron Collider.[1] IR optics collection LHC. a significant amount of international collabowould be made to the proton injector. significant changes quirements. cost.[1][2] The resultant higher event rate poses important challenges for the particle detectors located in the collision areas.1 See also Super Proton Synchrotron (SPS) Upgraded: The present SPS would be substantially upgraded to handle an in120 • Particle physics • High Luminosity Large Hadron Collider . • A summary of the possible machine parameters can be found at Machine parameters collection.[1] A workshop was held in 2006 to establish which are the most promising options. and power reAs part of the Phase 2 Super LHC.1 Super Large Hadron Collider creased beam intensity from PS2. And it would require a tunnel 80–100 kilometres around. 6. there has been little research money available worldwide to develop the concept.2. The New York Times. James (10 July 2001).6. compared with the planned 14 TeV of the LHC at CERN. on Next Collider”. at the Snowmass meeting in Minneapolis. For the past decade or so.org. Minnesota — where hundreds of particle physicists assembled to dream up machines for their field’s long-term future — the VLHC concept stood out as a favourite. Retrieved 27 June 2009. “Physicists plan to build a bigger LHC”. Nature News. VERY LARGE HADRON COLLIDER 6. compared with the LHC’s 27-km circumference. But this summer. Europe’s particle-physics lab near Geneva in Switzerland. retrieved 2013-12-03.2. Eugenie Samuel (2013-11-12). “Physicists Unite. [2] Reich.2 References [1] Glanz. a Fermilab webpage on VLHC research and development • VLHC Design Materials 121 . Sort of.3 External links • vlhc.2. It would collide protons at energies around 100 teraelectronvolts (TeV). The giant machine would dwarf all of its predecessors. CredoFromStart. RandomAct. Ronark. Wolvve85. Douglas the Comeback Kid. Bevo. Empty2005. Hugh Mason.saleh. Legobot. Aaker. Andrejj. Fsiler. Zagalejo. Debresser. Che090572. Bsegal. Jim1138. Af648. Ospalh. A. DV8 2XL. Stringer1993. Zumalabe. EmausBot. TedE. Dumelow. Pvosta. Chstens. Download. Gwern. StewartMH. Cydebot. Kencf0618. Kusunose. Airplaneman. Venske. Notheruser. Brianann MacAmhlaidh. Christian List. Engmark. SheffieldSteel. Zzyzx11. Gpanda. Jll. JT Swe. Snorgle. Poptropica. TjBot. Khukri. StaticGull. Chris the speller. Lord British. Naudefjbot. Yinchongding. Itai. Raxxel. Addshore. Yobot. Luminite2. Hemlock Martinis. Tkessler. Forthommel. LilyKitty. KPH2293. Srleffler. Clappyyay. Addbot. Drbrain. Ms2ger. Azileron. Aspects. Wavelength. DagosNavy. Krashlandon. BRW. di M. Frecklefoot.1 Text • CERN Source: http://en. Jauerback. Doomsday28. GrouchoBot. 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Shantanu28Editor. Akro7. Tushar. PSimeon. Vieque. Flatfatmat. Adejam. ZéroBot. Tetra quark and Anonymous: 1373 • List of Large Hadron Collider experiments Source: http://en. SCZenz. Tayste. Snacks. TarzanASG. Wikipelli. Chrisrus. Rich Farmbrough. GetTheShift. Rhlozier. Maxime. Mimihitam. AvocatoBot. Cannolis. Eio. A. RedBot. Colmsherry. Wikidokman. Lumidek. ClueBot NG. Cyberia23. Tictac66. RA0808. IceUnshattered. Ever388. SD5. Khukri. Rjwilmsi. Wisconsinbadger. Hamid26747. Michaelmas1957. Mean as custard. Tmckeage. Mspraveen. THMRK1. OnlyShadab. The Thing That Should Not Be. Seeleschneider.hatzifotiadou. Fl4ian. Csmallw. Boone jenner. Bibcode Bot. Mark Schierbecker. Versus22. Ptbotgourou. CensoredScribe. Piggyspider123. Mgambentok. Lenary. Donfbreed. DumZiBoT. Jeffrey Mall. Antimatter Dilbert. Stephen Poppitt. Fraggle81.bhatnagar. Advertiseo. Muhammedpbuh. Locobot. NeoTheChosenOne. Apparition11. Sun Creator. . LaaknorBot. FrescoBot.Interval. FrescoBot. VolkovBot. MrOllie. Lukealanjohnson. di M. Pcharito and Anonymous: 51 • ATLAS experiment Source: http://en. SPat. Kmchanw. Eothred. RjwilmsiBot. Hhhippo. AvalonTreman. Lets Enjoy Life. Mnmngb. OllieFury. Tomásdearg92.co. Philippe BINANT. Anbu121. HisNameIsChris. Citedegg. Calmyourfarm. WPratiwi. Polishhill. InternetMeme. Everyme. Titodutta. W Nowicki. Tbhotch. Atif. WannabeAmatureHistorian. LonelyMarble. KrazyKelle. Citation bot. PooRadley. PointOfPresence. संजीव कुमार. NameIsRon. AndrewWatt. Lupin. Randy Kryn. I dream of horses. Stickee. CXCV. One. ClueBot NG. Manu-ve Pro Ski. Giu8888. Bmoc2012tms. Willknowsalmosteverything. Kuber Kanade. Hj FUN. Chryst Laxus.124 CHAPTER 7. DoctorJoeE. Gflashwnox. Eeekster. Spinoff. Delusion23. ChrisGualtieri. Andrius. Xqbot. Narutolovehinata5. Sdedeo. TobeBot. BG19bot. 84user. Mentisock. Lethesl. Barak Sh. Tide rolls. Spellage. AndyHe829. NORD74. Athul av. Martinvl. Polaroids4x5. The Firewall. Nukes4Tots. Abcadi. QuadrivialMind. Prestonmag. Chriss789. Idioma-bot. Mrdressup. Jóhann Heiðar Árnason. CONTRIBUTORS. Hickorybark.wilton. Hamiltondaniel. Nacre 10. Pinethicket. Wonderflash1111. Dacool7. Econ oh my. Swagit420. Beta Orionis. Capricorn42. Florentino floro. Pyfan. QuantumAmyrillis. Jag123. Emily Jensen. Magog the Ogre. Coasterlover1994. Rues. Kyurkewicz. Gourra. EuroWikiWorld. Susvolans. Bubba73. Deagle AP. Gedankenpause. ScAvenger.nr. AkhtaBot. Orion11M87. Kyle the bot. Cvet. Dewritech. NellieBly. GorillaWarfare. Mitch Ames. Reatlas. Amorsch. Rob. GrandDrake. Legobot II. Sfsupro. Trotter. GuyanaMan. Meno25. Ottre. SidKemp. ScottSteiner. Omnipaedista. Mfb. LeoNomis. Mfb. Electron9. Metricopolus. Ebehn. GrouchoBot. Larosch. Slashme. Techieb0y. Luckas-bot. AndersBot.1. SCZenz. Goudzovski. SmackBot. Mark Williamson. Maurice Carbonaro. Addbot. Ptbotgourou. Justice Marshall. Vanished user 47736712. LeoNomis. LeoNomis. Creidieki. NearlyDrNash. Echoray. XLinkBot. Slyatslys. NotWith. Sheliak. Ptbotgourou. JabberWok. NotWith. Ssayler. AHusain314. Kiki 233. Cynicism addict. Citation bot 1. Jbond00747. SieBot. Ttquer.Hull. Lzur. Plasticup. Edward. Fabricebaro. Rama.org/wiki/Compact%20Muon%20Solenoid?oldid=650630597 Contributors: Michael Hardy. Goudzovski. Lightbot. Themisb. Dirac1933. Headbomb. Penguin.wikipedia. Newty23125. Rich Farmbrough.. Luckas-bot. WISo. Sheliak. Nick Number. Rich Farmbrough. MenoBot. CaptinJohn.wikipedia. Kolbasz. LucienBOT. Bobbias. Mark Williamson. Jmnbatista. FayssalF. Addbot. Larosch. GraemeL. Bornerdogge. Kourkoumeli. Khukri.org/wiki/Beetle%20(ASIC)?oldid=532577308 Contributors: Gary. Larosch. DJIndica. Sun Creator. XLinkBot. Headbomb. Oswald le fort. Mild Bill Hiccup. MindZiper. Cougarsoul.org/wiki/Worldwide_LHC_Computing_Grid?oldid=648476718 Contributors: Edward. The Anome. RJFJR. Sim@simpol. EmausBot. Juhanson.org/wiki/Proton%20Synchrotron%20Booster?oldid=593082473 Contributors: Laurascudder. RussBot. AndyHe829. Anderson. Dirk P Broer. Chobot. JMacalinao. AugPi. SirNewtonNinegames. Linas. 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Johantheghost. The Anomebot2. Headbomb. Headbomb. GrouchoBot. Timetraveler3. IG-64.7. Citation bot 1. Srich32977. TaiSakuma. Isis. Sheliak. Bridgeplayer. Turnstep. Headbomb. Addbot. Mütze. A1056207. Joopercoopers. TXiKiBoT. D'ohBot. SebastianHelm. SCZenz. Cobaltbluetony. Ttquer.wikipedia. TriTertButoxy. SmackBot. Linas. Keenan Pepper. Mdneedham. Looxix. Boud. Dawynn. Hellcat fighter. Davdde. Julesd. RibotBOT. Craigallan. GraemeL. Wdfarmer.harutyunyan and Anonymous: 16 • Proton Synchrotron Booster Source: http://en. Bibcode Bot. Archon 2488. Xqbot. Lightbot. MauritsBot. 100110100. Thijs!bot. Sheliak. AnomieBOT. WISo. Cgingold. Ed Poor. DASHBot. Bibliophilen. Pip2andahalf. WikitanvirBot. Sheliak. Laurascudder. BG19bot. Dirc. Eyreland. Bovineone. Tkolberg. Heylarson. Archon 2488. Nevit. SmackBot.org/wiki/LHCb?oldid=650630652 Contributors: Harp. Amirobot. Citation bot. Bibcode Bot. Ysangkok. Mfb and Anonymous: 27 • Standard Model Source: http://en. Srich32977. Erier2003. Cowman109. BillinSanDiego. Cgingold. SmackBot. Kyurkewicz. CommonsDelinker. Steve Quinn. WOSlinker. PalNilsson70. Sheliak. Andrius. Headbomb. LucienBOT. Rapsar. Timetraveler3. Pkoppenb. Yobot. Pleroma. Minimac. Bobo192. Herr apa. Laurascudder.wikipedia. AndersBot. TGCP. SandyGeorgia. Amakuru.v.org/wiki/Standard%20Model?oldid=648576968 Contributors: AxelBoldt. Roadrunner. Jmnbatista. Yobot. Andrius. Kyurkewicz. SkywalkerPL. Francoroldan. Davdde. Cowgoesmoo2. SpaceKangaroo. Spike Wilbury. Alessia2703. Citation bot 1. TAnthony. Djinn65. Walkingstick3. P199. Turnstep. Kyle the bot. SmackBot. MartinGrunewald. GimmeBot. SieBot. January2009. AndyHe829. Orion11M87. Jll. Wikiacc. Addbot. Rich Farmbrough. Bkell. Gene Nygaard. Cburnett. Icalanise. WPratiwi and Anonymous: 10 • FP420 experiment Source: http://en. Pakaraki. Wwoods. Erkcan. Adrian 1111. Puzl bustr. Tm1729. Suruena. Freeboson. Minghong. LeoNomis. Remuel. Keenan Pepper. Johantheghost. Ebehn. LeoNomis. Bibcode Bot. Valodzka. Alby. Nonnormalizable. Cydebot. Mets501.org/wiki/FP420%20experiment?oldid=650627020 Contributors: Thomas Blomberg. Bibcode Bot. Spellmaster. LeoNomis. Xqbot. DumZiBoT. AndyBuckley. MenoBot. . Orion11M87. Yobot. Angelastic. Alberthuang2. Mxn. David spector. David Biddulph. Leighperson. Noderaser. Mattgirling. Harp. YurikBot. Chronitis. Eshmo.jan. Patrick. Mütze. Khukri. Hex87. PipepBot. Bzzybee13. RibotBOT. Water Bottle. CXCV. V9. WISo. Professorolous. Alynna Kasmira. PanacheCuPunga. Gamer007.org/wiki/LHCf?oldid=650630864 Contributors: Rich Farmbrough. Billion. Mallorn.wikipedia. Kinhull. Magioladitis. Khukri. Alaibot. AnomieBOT. Ethyr. Archon 2488. Ram-Man.org/wiki/TOTEM?oldid=650630800 Contributors: Philopp. Jll. SCZenz. AvicAWB and Anonymous: 3 • LHC Computing Grid Source: http://en. VolkovBot. Neparis. Tiki2099. Ciphers. Robfloop.snoopy. AcademyAD.14. Mnmngb. Woodrowr. Laurascudder. Youandme. Pkoppenb. Jmnbatista. Yobot. Nanite. Headbomb. Kyurkewicz. Conscious. Toffile. Lightbot. Bibliophilen and Anonymous: 9 • Beetle (ASIC) Source: http://en. Ida Shaw. Zwobot. Spellage. Luckas-bot. Welsh. Col. Michael Hardy. Smite-Meister. DOI bot. Luckas-bot. Andre Engels. Giftlite. Jjhat1. Simon Villeneuve. Mr. AndyHe829. Bender235. Kozuch. Beno1000. Falcorian. Hyperfunnel. Nick. Giraffedata. GregorB. Bibliophilen. Xqbot. Slathering. GrahamHardy. ConejitaDo and Anonymous: 75 • LHCb Source: http://en. 7segment. Herbee. Pstanton. Fifieldt. Hekerui. Δζ. Eleveneleven. WISo. Alexbot. Spike Wilbury. Bombersun. Khukri. TXiKiBoT. Luckas-bot. Heliotropia. Alexbot. Bovineone. Bibliophilen. Idioma-bot.za. Fuenfundachtzig. . Bped1985. RoyBoy. Headbomb. Alaibot. Everyme. Giftlite. Amapelli. YiFeiBot and Anonymous: 28 • LHC@home Source: http://en. Hhhippo. Heliotropia.14. Rettetast. Javachan. Magioladitis. Kaspar. Ryan Roos. Rtomas. Omnipaedista. Bibliophilen. Idioma-bot. Z6. Headbomb. Ellipapa and Anonymous: 3 • TOTEM Source: http://en. Monkbot and Anonymous: 87 • Compact Muon Solenoid Source: http://en. GabeIglesia. TXiKiBoT. Falcorian. Javachan. SieBot. Steve Quinn. Headbomb. JenCawe. Kuru. Zorrobot. Davdde. DumZiBoT. Bryan Derksen. ShardsOfUs.org/wiki/LHC%40home?oldid=613568574 Contributors: Ilyanep. NotinREALITY. Bibcode Bot. Visée. Harris. Addbot. EmausBot. Khukri. Sheliak. Besselfunctions. AnomieBOT. Steve Quinn. Addbot. Rjwilmsi. Murielvd. Citation bot 1.net. Chandrasonic. Topperfalkon. W Nowicki. AndyBuckley. Glenn. Legosock. Kyurkewicz. Akro7. Laurascudder. DJIndica. Barry m. Mjaekel. Remuel. P199.wikipedia. Gortu. SinWin. Zorrobot. Conscious. . LaaknorBot. Kocio. JukoFF. Superm401. Metricopolus. Mdneedham. Reality3chick. Bibliophilen. SchroCat. VanishedUserABC. Citation bot. Themisb. Idiomabot. Davdde. Moritz37. Mortense. Citation bot 1. Qking. Netrapt. Xqbot. Thijs!bot. Fuenfundachtzig. Jcw69. Laurascudder. Conscious. OlEnglish. Rich Farmbrough. TEXT 125 Mithridates. MagdaGa. Addbot. Addbot. Citation bot. Ligulembot. AnomieBOT. Derek Ross. Twigboy. Archon 2488. Tony1. Reddi. Eskimbot. Martijn Hoekstra. Isnow. GeneralBelly. Beyazid. Laurascudder.wikipedia.wikipedia. Artem. OrphanBot. Alexbot. DorganBot. TXiKiBoT. CYD. Erkcan. Bender235. Rsquid. SassoBot. Vanished user lkdofiqw39ru239jwionwcihu8wt4ihjsf. Wbm1058. BOT-Superzerocool. Populus. Ojs. Erkcan. Francphy5. Nick. Harp. Concord113. Khukri. Thijs!bot. False vacuum. Khukri. Amirobot. CaptinJohn. FrescoBot. Rich Farmbrough. AB. Harryboyles. L3bl4nc. RJFJR. Bruce89. VolkovBot. VolkovBot. Jimbrooke. The Anomebot2. Idioma-bot. GabeIglesia. VolkovBot. Anrnusna. Gaius Cornelius. Caco de vidro. GrouchoBot. Ekjon Lok. APH. Swpb. Elodzinski. Lee Daniel Crocker. LordAnubisBOT. Dexbot. Hectorthebat. Mignon. DerNeedle. Bamkin. Delbert7. Pierre Boreal. Harrigan. Innotata. QMarion II. LinkFA-Bot. Citation bot 1. Austin Maxwell. Kocio. Oxymoron83. Eeekster. Trelvis. Sonjaaa. Mark Schierbecker. Thijs!bot. Gnomon Kelemen. Tarcieri. O. Karol Langner. 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Len Raymond. Verdy p. DHN-bot. Dbraize. JimVC3. TenOfAllTrades. APH. ChrisGualtieri. Itinerant1. Tpbradbury. R. Fieldday-sunday. Addshore. News0969. Complex (de). Arthur Rubin. A. Kocio. Bongwarrior.wikipedia. Orpheus. Ch2pgj. Immunize. ChuispastonBot. VictorFlaushenstein. Melchoir. Mako098765. Bobo192. Hexane2000. Martarius. Inwind. NellieBly. Theopolisme. FrankTobia. Abid931. DumZiBoT. MovGP0. Stannered. CloudNineAC. PhoenixFlentge. Sjakkalle.delanoy. YurikBot. Helpful Pixie Bot. Zorrobot. Alansohn. Fatphil. J. Dcirovic. Dstudent. Kakofonous. Agasides. JabberWok. H2g2bob. Mamizou. Sijothankam. Addbot. Complexica. GrinBot. Alansohn. Snotbot. BR84. Non-dropframe. Awren. J Milburn. MTSbot. Raul654. Party.. Klilidiplomus. Vanished user fijw983kjaslkekfhj45. Ownedroad9. TXiKiBoT. Tirebiter78. Physicist brazuca. StarryGrandma. Tobias Bergemann. Lvwarren. A. Tfnewman. Yevgeny Kats. DannyWilde. CRKingston. Wbellido. ChrisGualtieri. Escalona. Brandonlovescrashincastles. Ohwilleke. Piyush Sriva. Maurreen. Monedula. Faethon34. Unyoyega. Oldnoah. D. Jung dalglish. Addbot. Thrawn562. Savidan. Phy1729. DragonBot. Mwoldin. Smeagol 17. Abjiklam. Silly rabbit. Iomesus. DerHexer. Glenn. NuclearWinner. Euan Richard. Jozwolf. Tonypak. FrescoBot. Pleroma. Bgwhite. Atlant. TallMagic. SimonMayer. Luckas-bot. Le sacre. Novacatz. Khazar2. Mindmatrix. MonoAV. Chrislk02. Geremia. Luckas-bot. Kacser. MichaelMaggs. Superwj5. Voidxor. DragonBot. Jamesontai. Egg. Techraj. Brews ohare. Lathamboyle. I9Q79oL78KiL0QTFHgyc. Garyzx. Ark. Mjamja. Byelf2007. Urvabara. Kowtje. Srleffler. Ironboy11. MK8. R. Ohconfucius. Leyo. Selkem. Stephen Poppitt. Gareth Owen.org/wiki/Particle%20physics?oldid=650161462 Contributors: AxelBoldt. Saeed. Physics therapist. Giftlite.. JaGa.com. Deepmath. Mouse7525. Seaphoto. JhsBot. BernardZ. Wavelength. PhySusie. HeptishHotik. Materialscientist. Dimension10. Dna-webmaster. Snigbrook. HEL. Nigstomper. Bamkin. Dratman. Goodnightmush. Xezbeth. J. Escarbot. Lukys. 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Billyfesh399. Gerakibot. Emijrp. The Epopt. Ragesoss. Aliotra. Blondietroll. Palfrey. Michael C Price. Citation bot. Drxenocide. Valenciano. Sirex98. Edward Z. The Transliterator. Scottfisher. Dv82matt. Wizardjr9o. Matthew Woodcraft. Bodhitha. Laurascudder. Quondum. George100. Wtmitchell. MJ94. MER-C. Likebox. Mcewan. Penarestel. Bambaiah. AgadaUrbanit. Roadrunner. Guy Harris. Alan Liefting. DWHalliday. Ryan Postlethwaite. clown will eat me. JulesH. Boing! said Zebedee. Qwertyus. RE. Nymf. FelixRosch. Ghalhud. Electriccatfish2.Nut. Someguy1221. Rjwilmsi. Arthena. Micraboy. Swamy g. Dfan. Jesse V. Arthur Smart. Dmmaus. Jgwacker. NuclearWarfare. Setreset. Maurice Carbonaro. Tycho. Fences and windows. ^demonBot2. Bennylin. Dev 176. Davemck. Lightbot. NjardarBot. ClueBot NG. Bm gub. Joshmt. Paine Ellsworth. Jmnbatista. SmackBot. ChristopherWillis. Ravi12346. Sodium. Mathewsyriac. Edsegal. Rich Farmbrough. Icalanise. Jim E. Fogger. Bookalign. Moritz37. Robofish. NawlinWiki. MoogleEXE. Head. Patrick. Pandacomics. Jason Quinn. Citation bot. Bubba73. Mpatel. Rholton. Almostcrime. Pt. Netrapt. Arcresu.. David Schaich. Qwerty Binary. Graham87. Van helsing. Michael Hardy. Jesse V. Phys. Pcd72. Diagramma Della Verita. PranksterTurtle. Tanner Swett. Palica. Caltas. Xqbot. Goudzovski. Bggoldie. BenRG. Mastertek. Battlemage. Billinghurst. Naraht. Mike2vil. AND LICENSES Haoherb428. Helpful Pixie Bot. RedBot. SCZenz. Olhp. SieBot. Ordovico. From That Show!. Dextrose. Wing gundam.. HorsePunchKid. Paine Ellsworth. RjwilmsiBot. Racerx11. Stapletongrey. Klortho. CYD. Aoosten. Michaelbusch. Daniel. Faethon36. Ginsuloft. Jotterbot. Physics. Jayanta mallick. Discospinster. El C. AgadaUrbanit. SheepNotGoats. JeffBobFrank. Dysepsion. Fuelbottle. JamieS93. Dominick. Smtchahal. Brim. Falconkhe. Bibcode Bot. Truthnlove. Texture. Tayste. Beta Orionis. Howie Goodell. Ilmari Karonen. Donzzz77. di M. Lupin. Zwobot. Benbest. Thunderboltz. Olexandr Kravchuk. Bevo. Bevo. Macumba. CWii. TEXT AND IMAGE SOURCES. RockMagnetist. CommonsDelinker. Tevatron. Ds13. SmackBot. Shawn in Montreal. Maurice Carbonaro. El C. IJVin. Mike Rosoft. Scrabby. Zekemurdock. Bender235. YurikBot. TaBOT-zerem. Reinoutr. Unconcerned.wikipedia. Thincat. CesarB. JayBeeEye. Slawojarek. Atomicthumbs. Asmeurer. MZMcBride. David Nicoson. Hvn0413. Almaionescu. Pulu. Bodera. Benplowman. SakeUPenn. Agharo. Akro7 and Anonymous: 13 • Supersymmetry Source: http://en. TobeBot. JabberWok. David spector. Kencf0618. C9. Vyroglyph. Closedmouth. Eddie Nixon. Francescog. Rolf h nelson. SqueakBox. Linas. Bambaiah. Gsard. Barak Sh. Karam.bunderson. Usp. Can't sleep. Gildir. La goutte de pluie. Puzl bustr. El C. Varlaam. Pharotic. MONGO. LovroZitnik. Phys. Endersdouble. Maarten van Vliet. Englishtest3. Monkbot. Drrngrvy. Giftlite. Robbot. Giftlite. Chetvorno. Bevo. Bgwhite. Jtuggle. Ylee. Bibcode Bot. Maxim Razin. BenRG. Citation bot 1. Natsirtguy. Famspear. Jgwacker. BenRG. Nihiltres. Englishcomptest. 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