CMS 실험을 통한 llgamma 최종 상태에서의 새로운 물리 현상 탐색

학위논문 (박사) -- 서울대학교 대학원 : 자연과학대학 물리·천문학부(물리학전공), 2020. 8. 양운기.This thesis presents a search for Zgamma resonances and a search for excited electrons and muons in llgamma final states at the LHC. The searches are based on a data sample of proton-proton collisions at a center-of-mass energy of 13TeV. The data were collected with the CMS detector in 2016 and amounts to an integrated luminosity of 35.9fb^-1. The observation is consistent with the standard model background prediction for both searches. Upper limits are set on the product of the production cross section and the branching fraction to Zgamma for narrow and broad resonance scenarios with masses between 0.35 and 4.0TeV. Besides, excited electrons and muons are excluded for masses below 3.9 and 3.8TeV, respectively, under the assumption that the excited lepton mass equals the compositeness scale. The best observed limit on the compositeness scale is obtained with an excited lepton mass of around 1.0TeV, excluding values below 25TeV for both excited electrons and muons.거대강입자가속기에서 Zgamma 공명과 들뜬 전자와 뮤온들이 llgamma 최종 상태로 생성되는 현상을 각각 탐색했다. 두 탐색에 쓰인 데이터는 질량 중심 에너지 13TeV에서의 양성자-양성자 충돌 데이터로써 2016년 CMS 검출기를 통해 수집한 35.9fb^-1에 해당한다. 관측 결과는 두 탐색에서 모두 표준 모형 예측과 잘 일치하였다. 좁은 Zgamma 공명 가설과 넓은 공명 가설 아래 생산단면적과 Zgamma로 붕괴하는 갈래비의 곱에 대한 상한을 공명 질량 0.35와 4.0TeV 사이에서 설정하였다. 들뜬 전자와 들뜬 뮤온의 경우 질량이 복합 규모와 같다는 가정 아래 각각 질량 3.9와 3.8TeV 미만이 배제되었다. 복합 규모에 대한 최선의 관측 하한은 들뜬 전자와 뮤온의 질량이 대략 1.0TeV인 경우에 25TeV로 주어졌다.Chapter 1 Introduction 1 Chapter 2 Theoretical Background 5 2.1 The Standard Model 5 2.1.1 Birth of Quantum Field Theory 5 2.1.2 Quantum Electrodynamics 6 2.1.3 Weak Interaction 9 2.1.4 Electroweak Symmetry Breaking 13 2.1.5 Higgs Yukawa Couplings 16 2.1.6 Flavor Physics 19 2.1.7 Quantum Chromodynamics 25 2.2 Physics Beyond the Standard Model 26 2.2.1 Extended Higgs Sector 27 2.2.2 Composite Higgs Models 30 2.2.3 Compositeness and Excited Leptons 31 Chapter 3 Experimental Setup 38 3.1 The Large Hadron Collider 38 3.2 The Compact Muon Solenoid Experiment 41 3.2.1 Coordinate System 44 3.2.2 Tracker 44 3.2.3 Electromagnetic Calorimeter 46 3.2.4 Hadron Calorimeter 48 3.2.5 Superconducting Solenoid Magnet 49 3.2.6 Muon Detector 50 3.2.7 Trigger and Data Acquisition 52 3.3 Event Reconstruction 53 3.3.1 Particle-Flow Reconstruction 54 3.3.2 Muon Reconstruction 55 3.3.3 Electron and PhotonReconstruction 57 3.3.4 Hadron Reconstruction 59 3.3.5 Jet Reconstruction 60 3.3.6 Semileptonic tau Lepton Decay Reconstruction 61 3.3.7 Missing Transverse Momentum Reconstruction 63 Chapter 4 Data and Simulated Samples 64 4.1 Data 64 4.2 Simulated Samples 66 4.2.1 Parton Distribution Function 66 4.2.2 Hard Process Generation 67 4.2.3 Parton Showering and Hadronization 68 4.2.4 Pileup Interactions 69 4.2.5 Detector Simulation 70 4.2.6 Signal Samples 72 4.2.7 Background Samples 73 Chapter 5 Event Selection 74 5.1 Electron and PhotonSelection 74 5.1.1 Isolation Criteria 74 5.1.2 Shower Shape Criteria 75 5.1.3 Electron Selection 76 5.1.4 Photon Selection 77 5.2 Muon Selection 77 5.3 Resonant Signal Selection 78 5.4 Nonresonant Signal Selection 80 Chapter 6 Background Modeling 81 6.1 Background for the Resonant Signal Search 81 6.1.1 Background Distribution in m_Zgamma 81 6.1.2 Bias Estimation 84 6.2 Background for the Nonresonant Signal Search 85 6.2.1 Major Backgrounds 85 6.2.2 Misidentified Photon Background Estimation 86 Chapter 7 Signal Modeling 92 7.1 Resonant Signal 92 7.1.1 Signal Distribution in m_Zgamma 92 7.1.2 Signal Selection Efficiency and Detector Acceptance 99 7.2 Nonresonant Signal 99 7.2.1 Search Window in m_lgamma^min-m_lgamma^max 99 7.2.2 Signal Selection Efficiency and Detector Acceptance 102 Chapter 8 Systematic Uncertainties 104 8.1 Systematic Uncertainties for the Resonant Signal Search 104 8.2 Systematic Uncertainties for the Nonresonant Signal Search 106 Chapter 9 Results 109 9.1 Statistical Interpretation 110 9.1.1 Likelihood and Nuisance Parameters 110 9.1.2 Maximum Likelihood Fit 111 9.1.3 Exclusion Limits 112 9.1.4 Significance 115 9.2 Results of the Resonant Signal Search 118 9.3 Results of the Nonresonant Signal Search 120 Chapter 10 Conclusions 126 초록 143Docto