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CP violating anomalous top-quark coupling in proton proton collision at √s = 13 TeV

  • 주제(키워드) LHC , CMS , CEDM , Top quark , CP violation , dilepton channel
  • 발행기관 고려대학교 대학원
  • 지도교수 최수용
  • 발행년도 2020
  • 학위수여년월 2020. 8
  • 학위구분 박사
  • 학과 대학원 물리학과
  • 세부전공 입자물리학
  • 원문페이지 194 p
  • UCI I804:11009-000000231909
  • DOI 10.23186/korea.000000231909.11009.0001171
  • 본문언어 영어
  • 제출원본 000046045886

초록/요약

Results are presented of a search for CP violation in top quark pair production, using proton-proton collision data at a center-of-mass energy of 13 TeV. The data set analyzed corresponds to an integrated luminosity of 35.9 fb−1 collected by the CMS experiment. Final states with two charged leptons are considered. In this search, two observables are probed, O1 and O3, which are the Levi-Civita tensors of the four-momenta of charged leptons, b quark jets, and top quarks. Asymmetries in these observables are sensitive to CP violation, and their measurement is used to determine the chromoelectric dipole moment (CEDM) of the top quark. The CEDMs derived from the measured asymmetries in O1 and O3 are 0.64±0.73(stat)±0.75(syst) and −0.39±0.78(stat)±0.75(syst) (×10−18gs · cm), respectively, with gS the strong coupling. These results are consistent with the standard model prediction.

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목차

Abstract
Contents i List of Figures v List of Tables xi
1 Introduction 1
2 Theoretical Overview 5
2.1 StandardModel................................. 5
2.1.1 TheElectroweakInteraction...................... 7
2.1.2 StrongInteraction ........................... 9
2.2 TopQuarkPhysics............................... 10
2.2.1 ThettProduction ........................... 10
2.2.2 TheDecayoftt............................. 11
2.3 CPviolatinganomaloustopquarkcouplings . . . . . . . . . . . . . . . . . 12
2.3.1 CPViolation .............................. 12
2.3.2 ElecticDipoleMoment......................... 14
2.3.3 CP violating anomalous top-quark couplings (CEDM) . . . . . . . 15
3 THE LHC and CMS Apparatus 19
3.1 TheLargeHadronCollider .......................... 19
3.2 TheCompactMuonSolenoid ......................... 22
3.2.1 TheCMSCoordinateSystem..................... 22
3.2.2 SuperconductingSolenoidMagnet .................. 24
3.2.3 TrackingDetectors........................... 25
3.2.4 ElectromagneticCalorimeter ..................... 27
3.2.5 HadronicalCalorimeter ........................ 29
3.2.6 TheMuonSystem ........................... 30
3.2.7 TriggeringSystem ........................... 32
4 Event Reconstruction and Object Reconstruction 35
4.1 ParticleFlowAgorithm ............................ 35
4.2 TracksandPrimaryvertices.......................... 36
4.3 ElectronReconstruction ............................ 37
4.4 MuonReconstruction ............................. 39
4.5 JetReconstruction ............................... 40
4.5.1 JetEnergyScale ............................ 40
4.5.2 Jet Energy Resolution (Jet Energy Smearing) . . . . . . . . . . . . 41
4.6 Identificationofjetsoriginatingfrombquarks . . . . . . . . . . . . . . . 42
4.7 METReconstruction.............................. 44
5 Analysis Procedure 47
5.1 AnalysisStrategy................................ 47
5.2 DataandSimulatedEventSamples...................... 48
5.2.1 Data................................... 48
5.2.2 Simulation ............................... 49
5.3 ObjectSelection ................................ 54
5.3.1 TriggerSelection ............................ 54
5.3.2 PrimaryVerticesSelection....................... 55
5.3.3 MuonSelection............................. 55
5.3.4 Electrons ................................ 57
5.3.5 Jets ................................... 58
5.3.6 b-quarkjetidentification........................ 59
5.3.7 MissingTransverseMomentum(MET). . . . . . . . . . . . . . . . 59
5.4 EventSelection................................. 61
5.5 EventReweighting ............................... 62
5.5.1 PileupReweighting........................... 63
5.5.2 LeptonScaleFactors.......................... 64
5.5.3 b-taggingProbability.......................... 64
5.6 BackgroundEstimation ............................ 68
5.6.1 DeterminationofDrell-YanBackground . . . . . . . . . . . . . . .
68 5.7 TopReconstruction............................... 71
5.7.1 Description of Algorithm of Kinematic Reconstruction . . . . . . . 71
5.7.2 PerfomanceofKinematicReconstruction . . . . . . . . . . . . . . 77
5.8 EventYields .................................. 78
5.9 ControlPlots .................................. 81
5.9.1 ControlPlotsfortheμ+μ−channel.................. 81
5.9.2 ControlPlotsforthee+e−channel .................. 85
5.9.3 ControlPlotsforthee±μ∓channel .................. 89
5.10 DistributionofPhysicsObservables...................... 93
5.11ExtractionofAsymmetry ........................... 96
5.11.1 PredictionofAsymmetry ....................... 96
5.11.2 LikelihoodFitMethod......................... 101
5.11.3 ExtractedAsymmetries ........................ 102
5.12SystematicUncertainty ............................ 103
5.12.1 DescribtionofSystematicUncertainties . . . . . . . . . . . . . . . 103
5.12.2 TableofSystematicUncertainties................... 108
5.13 AdditionalUncertaintiesofSystematicSources . . . . . . . . . . . . . . . 115
5.13.1 JetAngularResolution ........................ 115
5.13.2 ChargeMisidentification........................ 116
5.13.3 A Different Calorimeter Response to b/b Quark Jets . . . . . . . . 124
5.13.4 SummaryofDilution.......................... 129
5.14CombinationofAsymmetries ......................... 130
5.14.1 BLUEMethod ............................. 130
5.14.2 Combination .............................. 131
5.14.3 CominedUncertaintieswithBLUEMethod . . . . . . . . . . . . . 132 5.15SummaryofCPViolatingAsymmetry.................... 137
5.16 Extraction of CEDM (Chromoelectric Dipole Moment) . . . . . . . . . . . 139
5.16.1 ProuctionofCPViolatingEvents .................. 139
5.16.2 Prediction of Asymmetries with CP Violating Events . . . . . . . . 140
5.16.3 Linear Correlation Between dtG and Asymmetries . . . . . . . . . 148
5.16.4 ProcedureofExtractionofCEDM .................. 148
5.16.5 ExtractedCEDM............................ 153
6 Conclusion 155
7 Appendix 157
7.1 Study of statitical fluctuations in systematic uncertainty study . . . . . . 158
7.2 ADifferentCalorimeterResponsetob/bQuarkJets . . . . . . . . . . . . 161
Bibliography 163
Acknowledgement


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