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研究生:周品君
研究生(外文):Pin-Chun Chou
論文名稱:在 Belle 實驗中尋找 B0 介子衰變至 X(3872) γ 之分析
論文名稱(外文):Search for B0 → X(3872) γ at Belle experiment
指導教授:張寶棣
指導教授(外文):Pao-Ti Chang
口試委員:王名儒徐靜戈張敏娟王正祥
口試委員(外文):Min-Zu WangJing-Ge ShiuMing-Chuan ChangChung-Hsiang Wang
口試日期:2019-06-24
學位類別:碩士
校院名稱:國立臺灣大學
系所名稱:天文物理研究所
學門:自然科學學門
學類:天文及太空科學學類
論文種類:學術論文
論文出版年:2019
畢業學年度:107
語文別:英文
論文頁數:121
中文關鍵詞:B 介子稀有 B 衰變Belle 實驗X(3872)
DOI:10.6342/NTU201901047
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本篇論文在 Belle 實驗中尋找 B0 → X(3872)(→ J/ψ π+ π−)γ 之衰變。分析數據來自日本高能加速器研究機構 B 介子工廠(KEKB)在能量不對稱之正負電子對撞器中所蒐集,來自 Υ(4S) 衰變的 772 百萬 BB ̄ 介子對,其積分亮度為 711 fb^−1。本篇論文量測結果中並沒有發現顯著性的訊號,並得到了 90% 信心水準之下的衰變分支上限值為 B(B0 → X(3872) γ) × B(X(3872) → J/ψ π+ π−) < 5.1 × 10^−7。
We report the results of a search for the decay B0 → X(3872)(→ J/ψ π+ π−)γ. The analysis is performed on a data sample corresponding to an integrated luminosity of 711 fb^−1 and containing 772 × 10^6 BB ̄ pairs, collected with the Belle detector at the KEKB asymmetric-energy e+e- collider running at the Υ(4S) resonance energy. We find no evidence for a signal and place an upper limit of B(B0 → X(3872) γ) × B(X(3872) → J/ψ π+ π−) < 5.1 × 10^−7 at 90% confidence level.
口試委員會審定書 ii
Acknowledgements iii
中文摘要 v
Abstract vi
Contents vii
List of Figures xii
List of Tables xvi
Chapter 1 Introduction 1
1.1 Standard Model 1
1.2 B Physics 2
1.3 Charmonium and the X(3872) State 4
1.3.1 Charmonium States 4
1.3.2 Charmonium-like Exotic States 7
1.3.3 The X(3872) State 8
1.4 Motivation 10
Chapter 2 The Belle Experiment 12
2.1 KEKB Accelerator 12
2.2 Belle Detector 16
2.2.1 Beam Pipe and Beam-line Magnets near IP 17
2.2.2 Silicon Vertex Detector (SVD) 19
2.2.3 Extreme Forward Calorimeter (EFC) 20
2.2.4 Central Drift Chamber (CDC) 22
2.2.5 Aerogel Cherenkov Counter (ACC) 24
2.2.6 Time of Flight (TOF) 26
2.2.7 Electromagnetic Calorimeter (ECL) 28
2.2.8 KL and Muon Detector (KLM) 30
2.2.9 Solenoid Magnetic Field 31
2.2.10 Trigger and Data Acquisition System 31
Chapter 3 Event Selection and Reconstruction 35
3.1 Data Samples 35
3.1.1 Signal Monte Carlo 35
3.1.2 Background Monte Carlo 36
3.2 Event Selection 36
3.2.1 Photon Selection 36
3.2.2 Charged π Selection 37
3.2.3 J/ψ Selection 37
3.2.4 Reconstruction of X(3872). 38
3.2.5 B0 Reconstruction 39
3.3 Kinematic Variables 40
3.4 Selections Summary 42
Chapter 4 Background Study 43
4.1 Overview of Backgrounds Study 43
4.2 Background Suppression 43
4.2.1 cosθB 44
4.2.2 Thrust angle 44
4.2.3 Sphericity 45
4.2.4 B flavor tagging quality q·r 46
4.2.5 Kakuno Super Fox-Wolfram (KSFW) 46
4.2.6 Other training input parameters 48
4.3 Best FOM 48
4.4 Best Candidate Selection 49
4.5 Summary 49
Chapter 5 2D Fitting 53
5.1 Introduction 53
5.2 PDF Modeling 54
5.3 Fitter Testing 57
5.3.1 ToyMC ensemble test for dimuon channel 57
5.3.2 Gsim ensemble test for dimuon channel 58
5.3.3 ToyMC ensemble test for dielectron channel 58
5.3.4 Gsim ensemble test for dielectron channel 59
5.3.5 Detailed Results of Ensemble Tests 60
Chapter 6 Control Sample Study 62
6.1 Introduction 62
6.2 B0→KS0 π+ π− γ 62
6.2.1 Event Selection 63
6.2.2 Background Suppression 63
6.2.3 PDF Modeling and Fitting 64
6.2.4 Calibration on PDF Shape 66
6.2.5 Conclusion 66
6.3 B0→J/ψ K0 67
6.3.1 Event Selection 67
6.3.2 Background Suppression 67
6.3.3 PDF Modeling and Fitting 68
6.3.4 Calibration on Background Suppression Efficiency 68
6.3.5 Conclusion 70
Chapter 7 Systematic Error Study 71
7.1 Tracking Uncertainty 71
7.2 Number of BB ̄ Pairs Uncertainty 71
7.3 Secondary Sub-decay Uncertainty 71
7.4 Charged Particle Identification Uncertainty 72
7.5 γ Identification Uncertainty 72
7.6 Background Suppression Uncertainty 73
7.7 π0 Veto Uncertainty 73
7.8 X(3872)→J/ψ ρ0 generation model 73
7.9 Uncertainties Only for Fitting Method 74
7.10 Uncertainties Only for Counting method 75
7.11 Summary of Systematic Errors 75
7.12 Summary for Calibration Factor 75
Chapter 8 Upper Limit Estimation 76
8.1 Counting Method 76
8.1.1 Calibration on Signal Box Efficiency 76
8.1.2 Expected Background in Signal Region 77
8.1.3 Expected Counting Results 78
8.2 Fitting Method 78
8.2.1 Uncertainty on PDF Modeling 79
8.2.2 Fitting bias 79
8.2.3 Expected Fitting Results 80
8.3 Dicision to use counting or fitting method 80
Chapter 9 Open Box Result 82
9.1 Counting Results 82
9.2 Fitting Results 83
Chapter 10 Conclusion 85
Appendix A Plots of Event Selections 86
Appendix B Plots of Variables for NeuroBayes Training 87
B.1 B0→X(3872) γ 87
B.2 B0→KS0 π+ π− γ 90
B.3 B0→J/ψ K0 92
Appendix C Fitting Plots for Control Samples 95
C.1 B0→KS0 π+ π− γ 95
C.2 B0→J/ψ K0 98
C.2.1 Dimuon channel 98
C.2.2 Dielectron channel 98
Appendix D Scattering Plots 102
D.1 B0→X(3872) γ 102
D.2 B0→KS0 π+ π− γ 104
D.3 B0→J/ψ K0 105
Appendix E Pull and Nsig Distributions for Signal Ensemble Tests 107
Appendix F Fitter Testing for Control Samples 110
F.1 B0→KS0 π+ π− γ 110
F.1.1 ToyMC ensemble test 110
F.1.2 Gsim ensemble test 111
F.2 B0→J/ψ K0 112
F.2.1 ToyMC ensemble test 112
F.2.2 Gsim ensemble test 112
Bibliography 114
Thesis Results Presented 121
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