A Trigger for long-lived coloured or charged exotics for future luminosities in ATLAS Master Thesis by Ursula Søndergaard Supervisor: Rasmus Mackeprang June 2010 Acknowledgements Thank you Rasmus Mackeprang for showing me the wonderful worlds of BSM and SMPs and it’s community, curiosities and fun people. If it were not for you I would not have written this thesis. Thank you (and Peter Hansen) also for giving me the opportunity to experience CERN on site and letting me come along to workshops, and for being a patient supervisor! I wish also to thank Sascha Mehlhase for excellent proof-reading, advice and sharing of experience, thanks to Morten for many good discussions and advice, thanks Esben for many cups of espresso brought to the table, special thanks to Stefania and Jørgen Beck for being very inspirational scientists, thanks to Lotte and Johan and Christian Ohm for great company at CERN, and thanks to the rest of the HEP group at NBI you have all been very nice, also the computing guys. Thanks to my other physics friends Majken, Terese, Karen, Catarina, Troels, Carsten, plus whoever I forget. Last and Biggest thanks to my dear Jacob. 1 Contents 1 Introduction 8 1.1 Introduction.................................... .8 2 Theoretical motivation 12 2.1 TheStandardModel ................................ 12 2.1.1 Overview of the Standard Model . 12 2.1.2 Symmetries................................. 14 2.1.3 Beyond the Standard Model . 15 2.1.4 Theoretical concerns of the Standard Model . 16 2.1.5 Observation of unexplained phenomena . 16 2.2 BeyondtheStandardModelmodels . 17 2.2.1 Stable massive particles in beyond Standard Model scenarios . 19 2.3 Cosmologicalsearches&limits . 19 3Experiment 21 3.1 The Large Hadron Collider . 21 3.2 Hadronic interactions and calorimetry . 24 3.2.1 Nuclearscattering ............................. 24 3.2.2 Hadronic calorimetry . 25 3.3 ATLAS ....................................... 26 3.3.1 Detectorparts ............................... 27 3.3.2 TheInnerDetector............................. 28 3.3.3 The electromagnetic calorimeter . 28 3.3.4 TheTileCalorimeter............................ 30 3.3.5 TheMuonSpectrometer.......................... 32 3.3.6 The Atlas trigger system . 34 3.3.7 Level-1 trigger . 34 2 CONTENTS CONTENTS 3.3.8 TheHigh-LevelTrigger .......................... 38 4 Trigger for Stable Massive Particles 40 4.1 Simulationofexperiments . 40 4.2 StablemassiveparticlesattheLHC . 41 4.2.1 Stable massive particle production . 41 4.2.2 Case Study Specifications . 42 4.2.3 Kinematics . 43 4.2.4 Interactions of heavy exotic hadrons . 46 4.2.5 Interaction of R-hadrons . 47 4.2.6 Samples . 48 4.3 Trigger for long-lived heavy exotics . 50 4.3.1 Event characteristics and R-hadron challenges . 50 4.4 Buildingthetrigger .............................. 52 4.4.1 Level 2 trigger chain for SMPs . 57 4.5 L1triggerresults ................................ 58 4.6 High-leveltriggerresults. 62 4.6.1 RoIresults ................................. 66 4.7 Ratebudget ..................................... 68 4.8 Conclusion ..................................... 77 5Appendix 79 5.0.1 Signalplots................................. 79 5.0.2 Background plots . 98 Bibliography 138 3 List of Figures 2.1 The particles of the Standard Model . 13 2.2 Vacuum polarization diagram . 15 2.3 Running of coupling constants . 17 2.4 Top and stop loop contributions to the Higgs Mass . 18 0 2.5 A gluino decaying to a χ1 through a virtual squark . 19 3.1 The Large Hadron Collider . 21 3.2 Bethe-Bloch..................................... 24 3.3 TheATLASdetector................................ 27 3.4 pseudorapidity .................................. 28 3.5 Sagitta........................................ 29 3.6 The accordion structure of the ATLAS LAr calorimeter . 29 3.7 ATLAS Hadronic Calorimeter . 30 3.8 Schematicviewofatilecalmodule . 31 3.9 Scintillatorelement............................. 31 3.10 Segmentation of modules in tilecal . 32 3.11MuonSpectrometer ............................... 33 3.12 L1 trigger Diagram . 34 3.13 TheATLASMuonTrigger............................ 36 3.14 Calorimeter Trigger . 37 3.15 Trigger sequence diagram . 38 3.16 Trigger Chain . 39 4.1g, ˜ t˜ and ˜b pairproductioncrosssectionw. limits . 43 4.2 β distribution ofg ˜ R-hadrons . 44 4.3 pT distributionofgluinoR-hadrons. 45 4.4 Number of hadronic interactions of R-hadrons in 2m iron . 48 4 LIST OF FIGURES LIST OF FIGURES 4.5 Absolute energy loss of SMPs in 1 m of iron . 51 4.6 Average percentage of events with critical β w/o η cut . 54 4.7 TileCal.timeres.vs.energy . 56 4.8 Energydep.inTileCalorimeter . 56 4.9 L1 efficiency for generic gluino 700 GeV . 59 4.10 L1 efficiency for generic gluino 1000 GeV . 59 4.11 L1 efficiency for intermediate gluino 700 GeV . 60 4.12 L1 efficiency for regge STOP 500 GeV . 60 4.13 L1 efficiency for regge sbottom 400 GeV . 61 4.14 L1 efficiency forτ ˜ m=152 GeV . 61 4.15 Tile Calorimeter Time-of-flight of truth-matched candidates . 63 4.16 β dist. of tile candidates forg ˜ of 700 GeV, generic interaction . 64 4.17 pT dist. of tile candidates forg ˜ of 700 GeV, generic interaction . 65 4.18 Transverse momentum dist. of tt¯ ......................... 66 4.19 Mass dist. of tile candidates forg ˜ of 700 GeV, generic interaction . 67 4.20 Relative background efficiencies, L1 XE items (ET ) . 69 ! 4.21 Relative background efficiencies, L1 TAU items . 69 4.22 Relative background efficiencies, L1 MU items . 70 4.23 Run 177540 specification summary. 70 4.24 Run 177540 luminosity. 71 4.25RatesofL1XEitems ............................... 72 4.26RatesofL1TAUitems.............................. 73 4.27RatesofL1MUitems ............................... 74 4.28 Rate of combined L1 TAU6 XE10 items . 75 4.29 L2 efficiencyofthreeL1seeds. 78 5.1 β dist. of tile candidates forg ˜ of 700 GeV, generic interaction . 80 5.2 β dist. of tile candidates forg ˜ of 1000 GeV, generic interaction . 81 5.3 β dist. of tile candidates forg ˜ of 700 GeV, intermediate interaction . 82 5.4 β dist. of tile candidates for t˜ of 500 GeV, regge interaction . 83 5.5 β dist. of tile candidates for t˜ of 500 GeV, regge interaction . 84 5.6 β dist. of tile candidates forτ ˜ of 152 GeV . 85 5.7 pT dist. of tile candidates forg ˜ of 700 GeV, generic interaction . 86 5.8 pT dist. of tile candidates forg ˜ of 1000 GeV, generic interaction . 87 5.9 pT dist. of tile candidates forg ˜ of 700 GeV, intermediate interaction . 88 5 LIST OF FIGURES LIST OF FIGURES 5.10 pT dist. of tile candidates for t˜ of 500 GeV, regge interaction . 89 5.11 pT dist. of tile candidates for ˜b of 400 GeV, regge interaction . 90 5.12 pT dist. of tile candidates forτ ˜ of 152 GeV . 91 5.13 Mass dist. of tile candidates forg ˜ of 700 GeV, generic interaction . 92 5.14 Mass dist. of tile candidates forg ˜ of 1000 GeV, generic interaction . 93 5.15 Mass dist. of tile candidates forg ˜ of 700 GeV, intermediate interaction . 94 5.16 Mass dist. of tile candidates for t˜ of 500 GeV, regge interaction . 95 5.17 Mass dist. of tile candidates for t˜ of 500 GeV, regge interaction . 96 5.18 Mass dist. of tile candidates forτ ˜ of 152 GeV . 97 5.19 Beta dist. of ttevents¯ ............................... 98 5.20 Betadist.ofQCDdi-jetevents . 99 5.21 Beta dist. of Z ττ ................................ 100 → 5.22 Beta dist. of Z µµ ................................ 101 → 5.23 Beta dist. of W τν ................................. 102 5.24 Transverse momentum dist. of tt¯ events . 103 5.25 Transverse momentum dist. of QCD di-jet events . 104 5.26 Transverse momentum dist. of Z ττ events . 105 → 5.27 Transverse momentum dist. of Z µµ . 106 → 5.28 Transverse momentum dist. of W τν . 107 → 5.29 Mass dist. of tt¯ ................................... 108 5.30 Mass dist. of QCD di-jet events . 109 5.31 Mass dist. of Z ττ ............................... 110 → 5.32 Mass dist. of Z µµ ............................... 111 → 5.33 Mass dist. of W τν ............................... 112 → 5.34 Run rates and prescales of L1 J items . 113 5.35RunratesofL1XEitems ............................ 113 5.36RunratesofL1MUitems............................ 114 5.37RunratesofL1TEitems ............................ 114 5.38RunratesofL1TAUitems ........................... 115 5.39 Perfomance of L2 SMP chain with L1XE20 forg ˜ of 700 GeV, generic interaction116 5.40 Perfomance of L2 SMP chain with L1XE20 forg ˜ of 1000 GeV, generic interaction model117 5.41 Perfomance of L2 SMP chain with L1XE20 forg ˜ of 700 GeV, intermediate interaction model118 5.42 Perfomance of L2 SMP chain with L1XE20 for t˜ of 500 GeV, intermediate interaction model119 5.43 Perfomance of L2 SMP chain with L1XE20 for t˜ of 400 GeV, intermediate interaction model120 6 LIST OF FIGURES LIST OF FIGURES 5.44 Perfomance of L2 SMP chain with L1XE20 for t˜ of 400 GeV, intermediate interaction model121 5.45 Perfomance of L2 SMP chain with L1TAU5 forg ˜ of 700 GeV, generic interaction122 5.46 Perfomance of L2 SMP chain with L1TAU5 forg ˜ of 1000 GeV, generic interaction model123 5.47 Perfomance of L2 SMP chain with L1TAU5 forg ˜ of 700 GeV, intermediate interaction model124 5.48 Perfomance of L2 SMP chain with L1TAU5 for t˜ of 500 GeV, intermediate interaction model125 5.49 Perfomance of L2 SMP chain with L1TAU5 for t˜ of 400 GeV, intermediate interaction model126 5.50 Perfomance of L2 SMP chain with L1TAU5 for t˜ of 400 GeV, intermediate interaction model127 5.51 Perfomance of L2 SMP chain with L1TAUXE5 forg ˜ of 700 GeV, generic interaction128 5.52 Perfomance of L2 SMP chain with L1TAUXE5 forg ˜ of 1000 GeV, generic