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A method for measuring CKM matrix element |Vcb| from top quark pair events at the LHC

  • 주제(키워드) CKM , LHC
  • 발행기관 고려대학교 대학원
  • 지도교수 최수용
  • 발행년도 2021
  • 학위수여년월 2021. 2
  • 학위구분 석사
  • 학과 대학원 물리학과
  • 원문페이지 60 p
  • UCI I804:11009-000000235427
  • DOI 10.23186/korea.000000235427.11009.0001163
  • 본문언어 영어
  • 제출원본 000046072193

초록/요약

Measurements of the Cabbibo-Kobayashi-Maskawa matrix elements are important tests of the consistency of the standard model. However, there is some tension in the |Vcb| measurements, depending on the final states used. The |Vcb| has been determined from the measured branching ratios of B-hadron to final states with c quarks. An independent method of measuring |Vcb| is needed to understand the cause of the discrepancies. We propose a new way of measuring |Vcb| at the LHC. It can be measured from decay of real W bosons W → cb, where the source of the real W bosons is the abundant tt sample. By applying b-tagging algorithms on jets from W → qq' , we can measure the fraction of W → cb present. With approximately 300 fb−1 of data, the significance is large enough to merit further development of the method.

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목차

Abstract
Contents i
List of Figures iii
List of Tables v
1 Introduction 1

2 Theoretical Overview 3
2.1 Standard Model................................. 3
2.2 CKM matrix .................................. 5
2.3 Top Quark ................................... 7

3 Experimental Setup 9
3.1 LargeHadronCollider ............................. 9
3.2 Compact Muon Solenoid detector....................... 11
3.2.1 Superconducting Solenoid ....................... 13
3.2.2 Tracking System ............................ 13
3.2.3 Calorimeters .............................. 13
3.2.4 Muon System.............................. 14
3.3 Monte Carlo Simulation ............................ 14
3.3.1 Madgraph................................ 16
3.3.2 Pythia.................................. 17
3.3.3 Delphes ................................. 17

4 Object Reconstruction and Event Reconstruction 20
4.1 Particle Propagation .............................. 20
4.2 Calorimeters .................................. 21
4.3 Particle Flow Reconstruction ......................... 22
4.4 Object Reconstruction............................. 22
4.4.1 Charged Leptons............................ 22
4.4.2 Jets ................................... 23
4.4.3 Missing Transverse Energy ...................... 25

5 Analysis 26
5.1 Method of |Vcb| measurement with top quark pairs . . . . . . . . . . . . . 26
5.2 Simulated data sample............................. 27
5.3 Event selection ................................. 28
5.4 kinematic reconstruction............................ 29
5.5 Expected Events yield and RF ̄ ....................... 34
5.6 RF ̄estimation................................. 35
5.7 Extraction of |Vcb| from top quark pair events . . . . . . . . . . . . . . . . 39
6 Conclusion 46
Bibliography 47

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