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研究生：	汪本璿 Pen-Hsuan Wang
論文名稱：	Search for Exotic Decay of A Higgs Boson into A Dark Photon and a Standard Model Photon in pp Collisions at √s = 13 TeV
指導教授：	郭家銘 Chia-Ming Kuo
口試委員:
學位類別：	碩士 Master
系所名稱：	理學院 - 物理學系 Department of Physics
論文出版年：	2018
畢業學年度：	106
語文別：	英文
論文頁數：	124
中文關鍵詞：	稀有希格斯衰變、緊湊渺子線圈、大強子對撞機緊湊渺子線圈
外文關鍵詞：	Dark photon, Exotic Higgs decay, Compact Moun Solenoid, Hidden sector
相關次數：	點閱：11 下載：0
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有關暗光子的理論主要是出自於早期天文物理觀測的結果與現有理論不符合，這些觀測結果指出新物理的存在。為了解釋觀測結果，理論學家延伸自標準模型 U(1)群，在 Hidden Sector 中建立了一個新的假設性的 U(1)群。暗光子為此假設性的 U(1)群的介子。歐洲核子物理研究所的大強子對撞機為目前世界上對撞能量最高且高亮度的質子質子對撞機，因此擁有龐大的潛能來尋找 GeV 質量尺度的暗光子。本篇論文利用質子-質子質心能量√s = 13 TeV 的對撞產生希格斯粒子，暗光子則藉由希格斯粒子的稀有衰變來產生，並且通過暗光子的渺子衰變頻道來尋找新的渺子-渺子對不變質量共振來尋找暗光子，此研究使用 2016 年全年度 CMS 所蒐集的資料進
行分析，總亮度為35.9fb-1。

The hypothesis of Dark Photon(ZD) is motivated by a number of astrophysi- cal observational anomalies which indicate the new physics beyond Standard Model(SM) is existing in our world. The Hidden Sector contains a hypothetical U (1)D gauge group is introduced by extension of the SM. The ZD is a theoretical particle which does not play a role as Dark Matter(DM) itself but play a role as gauge mediator of hypothetical hidden U(1)D gauge group. With the advent of the Large Hadron Collider(LHC), a powerful machine with unprecedented high central-of-mass energies and high luminosities gives the potential to probe the GeV scale ZD. The searches of ZD from exotic Higgs decays and decaying into a muon pair in pp collision with √s = 13 TeV is ongoing by looking for new dilepton invariant mass in sub-GeV scale. This analysis using full 2016 data recorded by CMS detector in integrated luminosity 35.9 fb−1.

Introduction and Theory Overview 1
1 Motivation................................ 1
2 The Dark Photon ............................ 2
2.1 The Kinematic Mixing ..................... 3 
2.2 The Production of ZD Via a New Vector-like Fermion Loop 4
2.3 The Production of ZD Via Kinematic Mixing in The SM H→ZγProcess ........................ 6
3 SignalSearchingandKinematic.................... 8
4 ReviewofZDSearches ......................... 10
The LHC and CMS detector 13
1 Large Hadron Collider ......................... 13
2 CMS Detector ............................... 14
2.1 Coordinate in CMS....................... 16 
2.2 Superconducting Magnet ................... 16 
2.3 Tracking System ........................ 16 
2.4 Electromagnetic Calorimeter ................. 18 
2.5 Hadron Calorimeter ...................... 20 
2.6 Muon System .......................... 20
3 Trigger System.............................. 24 
3.1 Level-1Trigger ......................... 24 
3.2 High Level Trigger ....................... 24
Analysis Strategy 27
1 Datasets and Monte Carlo samples.................. 28
1.1 Datasets ............................. 28
1.2 Monte Carlo Samples ..................... 28 
Signal samples ......................... 28
Background Samples...................... 33
2 Trigger .................................. 34
3 Objects Reconstruction and Identification . . . . . . . . . . . . . . 35
3.1 Vertex Reconstruction and Pile-up . . . . . . . . . . . . . . 35
3.2 MuonReconstruction ..................... 36 
Local Reconstruction...................... 36 
Global Reconstruction ..................... 37 
Particle Flow Muons...................... 38 
Muon Momentum Correction................. 38
3.3 Electron and Photon Reconstruction . . . . . . . . . . . . . 39 Clustering............................ 39 
Supercluster Energy Correction................ 40 
Fine Tuning of Photon Energy Scale and Smearing . . . . . 41
4 Objects Selection ............................ 42 
4.1 Muon  Selections ........................ 43 
4.2 PhotonSelections........................ 44
5 Events Selection............................. 45 
5.1 Higgs Mass Window Cut ................... 45 
5.2 ∆R(μ,μ)Cut .......................... 48 
5.3 Boosted Kinematic Cut..................... 50
6 Corrections on Monte Carlo Sample ................. 51
6.1 Pileup Reweighting ...................... 51
6.2 ID Scaling Factors........................ 52
Photon SFs............................ 53 
Double Muon Trigger SFs ................... 56 
Muon SFs ............................ 58
7 Selected Events from Data and Acceptance×Efficiency of MC Signal 60
Background and Signal Estimation 63
1 Background ............................... 63 
1.1 Sideband Control Region ................... 63 
1.2 Background Fitting....................... 65
2 Signal................................... 67 
2.1 FSR Recovery .......................... 68 
2.2 Signal Fitting .......................... 69
Systematic Uncertainties 71
1 Pileup Reweighting Uncertainty ................... 71
2 DoubleMuon Trigger Efficiency Uncertainty . . . . . . . . . . . . 72
3 Photon MVA ID Efficiency Uncertainty ............... 72
4 Muon ID Efficiency uncertainty.................... 76
5 Photon Energy Scale and Smear Uncertainties . . . . . . . . . . . 77
6 Muon Momentum Scale and Smear Uncertainties . . . . . . . . . 78
7 Background Shape Uncertainties ................... 81 
8 Total systematic uncertainty...................... 83
Result 85 
1 Cross Section×Branching Ratio Limit ................ 85 
2 Conclusion................................ 88
Bibliography 91
                                

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