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研究生：	張秋萍 Chiu-Ping Chang
論文名稱：	Search for a Higgs boson decaying into γ∗γ → eeγ in pp collisions at √s = 8 TeV with the CMS detector
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：	2015
畢業學年度：	104
語文別：	中文
論文頁數：	93
中文關鍵詞：	高能物理、希格斯粒子、粒子物理、大強子對撞機
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本篇論文研究希格斯玻色子衰變成一個虛擬光子和一個光子，其中虛擬光子衰變成正負電子對，本分析使用質子-質子對撞，能量在8TeV的對撞於LHC的CMS偵測器記錄到總和亮度為19.7/fb的數據。終態為兩個非常靠近的正負電子以及一個高能量的光子，正負電子因為太靠近彼此而無法在電磁量能器內分辨為二。本實驗的結果與另一個實驗結果相互結合：希格斯玻色子衰變成一個虛擬光子和一個光子，其中虛擬光子衰變成渺子對，結果顯示在 120 GeV 到 150 GeV 重建的希格斯玻色子的質量區間並沒有過量的訊號。觀察（預測）的訊號強度上限在質量為 125 GeV 時為 6.7 (5.9+2.8-1.8) 倍的標準模型預測。

A search is described for a Higgs boson decaying into two photons, one of which has an internal conversion to an electron pair (eeγ). The analysis is performed using proton-proton collision data recorded with the CMS detector at the LHC at a centre-of-mass energy of 8 TeV, corresponding to an integrated luminosity of 19.7/fb. The events selected have a merged electron caused by two close-by electrons from low mass γ* decay and a high transverse momentum photon.
The results are combined with H ->γ*γ -> μμγ final state, where dimuon mass below 20 GeV. No excess above background has been found in the three-body invariant mass range 120 < m(llγ) < 150 GeV.
The observed (expected) limit for Higgs mass = 125 GeV is about 7.62(9.97+4.81-3.10) times the SM prediction for H ->γ*γ -> eeγ, 10.79(7.59+3.78-2.36) times the SM prediction for H ->γ*γ -> μμγ and 6.7(5.9+2.8-1.8) times the SM prediction for combined channel.

Introduction and motivation 1
1 Standard Model.............................. 2
2 Higgs Mechanism............................. 4 
3 Review of the observation of Higgs boson .  . . . . . . . . . . . . . . 8 
4 Overview for H ->γ*γ -> eeγ ...................... 21
LHC and CMS detector 25
1 Large Hadron Collider .......................... 25
2 CMS detector............................... 28 
Analysis Procedures 41
1 Dataand Monte Carlo samples ..................... 41 
2 Trigger................................... 45
3 Objectrecon struction and selection ................... 45 
4 Event  selection .............................. 60
5 Background and signal modeling..................... 61
6 Systematic uncertainties ......................... 63
Results and conclusion 66
1 Crosssection limit computation ..................... 66 
2 Include H ->γ*γ -> μμγ ......................... 67 
3 Future plans................................ 69 
4 Conclusion................................. 69
                                

[1] CMS Collaboration. Observation of a new boson at a mass of 125 GeV with the CMS experiment at the LHC. Phys. Lett. B, 716, 2012.[2] ATLAS Collaboration. Observation of a new particle in the search for the stan- dard model Higgs boson with the ATLAS detector at the LHC. Phys. Lett. B, 716, 2012.
[3] A. Firan and R. Stroynowski. Internal conversions in Higgs decays to two pho- tons. Phys.Rev., D76, 2007.
[4] R. Oerter. The theory of almost everything: The standard model, the unsung triumph of modern physics (kindle ed.). ISBN 0-13-236678-9, page 2, 2006.
et al.

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