利用CMS探測器量測7TeV下的Zγ產生截面

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姓名

劉宗凱(Zong-Kai Liu) 查詢紙本館藏

畢業系所

物理學系

論文名稱

利用CMS探測器量測7TeV下的Zγ產生截面
(Measurement of Zγ production in pp collision at √s = 7 TeV with the CMS detector at the LHC)

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★ Measurement of Zγ production in 5 fb-1 of pp collisions at √s = 7 TeV with the CMS detector	★ Search for a Higgs boson decaying into γ∗γ → eeγ in pp collisions at √s = 8 TeV with the CMS detector
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摘要(中)

Zγ生產的量測能提供測試電弱理論結構的機會，也能給予新物理是否存在的線索。此篇論文利用CMS蒐集的 36 pb-1 的質子質子對撞數據，呈現了第一次在總碰撞能量7 TeV下的Zγ產生截面的量測，並選擇Z衰變為電子當作訊號事件。此產生截面量測是針對光子橫向能量大於10GeV，光子與電子空間上的分離ΔR(l, γ) 大於0.7，且輕子對恆定質量大於50GeV。量測的Zγ產生截面為9.5 ± 1.4（統計誤差）± 0.7（統計誤差）± 0.4（光度誤差）pb，與標準模型預測的Zγ產生截面9.6 ± 0.4 pb相符合。

摘要(英)

The measurement of Zγ production can provide an opportunity for examining the gauge sector of the Standard Model, and evidences for the existence of new physics. This thesis presents the first cross-section measurement of Zγ → e+e-γ at √s = 7 TeV using 36 pb-1 of proton-proton collision data collected by CMS. The cross-section is measured for the photon transverse energy ETγ > 10 GeV, spatial separation from charged leptons ΔR(l, γ) > 0.7 and dilepton invariant mass Mll > 50 GeV. The σ(pp → Zγ + X) × B(Z → e+e-) is measured to be 9.5 ± 1.4 (stat.) ± 0.7 (syst.) ± 0.4 (lumi.) pb, in agreement with Standard Model prediction of 9.6 ± 0.4 pb.

關鍵字(中)

★ 高能實驗

關鍵字(英)

★ CMS
★ di-boson

論文目次

摘要………………………………………………………………………i
Abstract…………………………………………………………ii
誌謝………………………………………………………………………iii
Contents…………………………………………………………iv
List of Figure…………………………………………vi
List of Table……………………………………………viii
Chapter 1 Introduction………………………………………………………1
Chapter 2 The CMS Experiment at LHC……………………4
2.1 The Large Hardon Collider…………………………………4
2.2 The Compact Muon Solenoid…………………………………5
2.2.1 Magnet……………………………………………………………………………6
2.2.2 Inner Tracker System………………………………………7
2.2.3 Electromagnetic Calorimeter……………………8
2.2.4 Hadronic Calorimeter……………………………………10
2.2.5 Muon System……………………………………………………………11
2.3 Trigger and Data Acquisition………………………12
2.3.1 Level-1 Trigger…………………………………………………13
2.3.2 High Level Triggers………………………………………13
2.4 Electron and Photon Reconstruction………14
2.4.1 Supercluster Reconstruction…………………14
2.4.2 Photon Reconstruction…………………………………15
2.4.3 Electron Reconstruction……………………………16
2.5 Luminosity measurement at CMS……………………17
Chapter 3 Overview of Zγ Production…………………21
3.1 Standard Model……………………………………………………………21
3.2 EWK Theory………………………………………………………………………22
3.3 Zγ Production and anomalous Triple Gauge Coupling…24
3.4 Review of Zγ Measurement…………………………………26
Chapter 4 Analysis Method……………………………………………28
4.1 Data and Monte Carlo samples………………………28
4.2 Anomalous signals in the ECAL……………………30
4.3 Object Identification…………………………………………33
4.3.1 Trigger………………………………………………………………………39
4.3.2 Electron Selection…………………………………………39
4.3.3 Photon Selection………………………………………………40
4.4 Measurement of efficiencies…………………………40
4.4.1 Tag and Probe Method……………………………………40
4.4.2 Electron reconstruction efficiency………………………42
4.4.3 Electron selection efficiency……………43
4.4.4 Trigger efficiency…………………………………………44
4.4.5 Photon reconstruction efficiency……45
4.4.6 Photon selection efficiency…………………46
4.4.7 Correction factor……………………………………………47
4.5 Background estimation…………………………………………49
4.5.1 Ratio Method…………………………………………………………49
4.5.2 Template Method…………………………………………………54
Chapter 5 Measurement of Zγ cross-section…60
5.1 Event selection…………………………………………………………60
5.2 Background estimation…………………………………………64
5.3 Cross-section measurement………………………………66
5.4 Systematic uncertainty………………………………………67
5.4.1 Systematic uncertainty on A×εMC………67
5.4.2 Systematic uncertainty on ρeff…………68
5.4.3 Systematic uncertainty on background estimation………68
5.4.4 Systematic uncertainty on Luminosity…………71
5.4.5 Summary of Systematic uncertainty…………………72
5.5 Result and comparison with theoretical prediction………72
5.5.1 Theoretical Prediction………………………………72
5.5.2 Results………………………………………………………………………73
Chapter 6 Conclusion…………………………………………………………76
Bibliography………………………………………………………………………………78
Appendix A Limits on Anomalous Trilinear Gauge Boson Couplings…82
Appendix B The Nuclear Compton Telescope (NCT) Project…………85

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指導教授

郭家銘、張元翰
(Chia-Ming Kuo、Yuan-Hann Chang)

審核日期

2011-7-13

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