Search for flavor changing neutral current in association with a top quark and a Z boson for the three lepton final state at √s = 13 TeV with CMS Run2 2016 data
질량 중심 에너지가 13 TeV 인 CMS Run2 2016년도 데이터를 이용하여 탑 쿼크와 Z 보존이 상호작용하는 지점으로부터 세 개의 렙톤을 가진 마지막 상태로 붕괴하는 경우를 이용한 맛을 바꾸는 중성류 과정의 탐색
- 발행기관 한양대학교
- 지도교수 김태정
- 발행년도 2021
- 학위수여년월 2021. 2
- 학위명 석사
- 학과 및 전공 대학원 물리학과
- UCI I804:11062-200000485712
- 본문언어 영어
- 저작권 한양대학교 논문은 저작권에 의해 보호받습니다.
초록/요약
The theme of the thesis is the search for the flavor-changing neutral current (FCNC) associated with a top quark and a Z boson for the three lepton final states. The proton-proton collision data collected in 2016 with centre-of-mass energy 13 TeV, an integrated luminosity is 36 fb-1 from the Compact Muon Solenoid (CMS) that is one of the general-purpose detectors at the Large Hadron Collider (LHC) are used for this analysis. The single top quark and top quark pair processes are considered to target signal in this search. Deviation of the FCNC signal from the standard model background is not observed. Observed (Expected) upper limits at 95% confidence level are set on the branching ratios of the top quark decays: Br(t→Zu) < 0.010%(0.010%) and Br(t→Zc) < 0.032%(0.027%)
more목차
1. Introduction 1
1.1. The LHC and the CMS detector 3
1.2. FCNC involving a tZq vertex 6
2. Datasets and Monte Carlo Samples 9
2.1. Datasets 9
2.2. Monte Carlo (MC) Samples 10
2.2.1. Signal Samples 10
2.2.2. Background Samples 10
3. Event Cleaning 13
4. Object Reconstruction and Event Selection 13
4.1. Object Reconstruction 13
4.1.1. Electrons 13
4.1.2. Muons 14
4.1.3. Jets 14
4.1.4. MET 15
4.2. Events Selection 15
4.3. Corrections of MC simulation 16
4.3.1. Pileup Reweighting 16
4.3.2. Lepton Scale Factors 17
4.3.3. Shape correction of jet from b-quark discriminator 17
4.3.4. Jet energy 17
4.3.5. Estimation of the trigger efficiency 18
5. Analysis Strategy 21
5.1. WZ Control Region (WZCR) 22
5.2. Single Top Control Region (STCR) and Top Pair Control Region (TTCR) 22
5.3. Single Top Signal Region (STSR) and Top Pair Signal Region (TTSR) 27
5.4. Result of Background Estimation with a Data-Driven 27
6. Signal Extraction 28
6.1. Kinematic Variable Reconstruction 28
6.2. Gradient Boosted Decision Tree (BDTG) in STSR and TTSR 29
7. Systematic Uncertainties 31
8. Result 35
8.1. Upper limits of branching ratio on tZc vertex 35
8.2. Upper limits of branching ratio on tZu vertex 36
8.3. Conclusion 37
Appendix A. Control plot 38
A.1. Step 2 38
A.2. Step 3 42
A.3. STSR 44
A.4. TTSR 53
Appendix B. The yield tables 62
B.1. Cut flow table by step 62
B.2. Table of signal regions and control regions 64
Appendix C. Gradient Boosted Decision Trees 67
C.1. Training variables and distributions 67
C.2. BDTG output distributions by lepton channel 68
C.3. Detailed result from TMVA 72
Appendix D. Systematic uncertainty shape effects 76
D.1. Effect to signal and backgrounds in STZct 76
D.2. Effect to signal and backgrounds in STZut 77
D.3. Effect to signal and backgrounds in TTZct 79
D.4. Effect to signal and backgrounds in TTZut 80
References 82
국문요지 88