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研究生：	吳承翰 Cheng-Han Wu
論文名稱：	Search for a Higgs boson decaying into \gamma^*\gamma \rightarrow ee\gamma with low dilepton mass in pp collisions at \sqrt{13} \sqrt{13} = 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：	2023
畢業學年度：	111
語文別：	英文
論文頁數：	122
中文關鍵詞：	希格斯粒子、虛光子、電子對
外文關鍵詞：	Higgs boson, virtual photon, electron pair
相關次數：	點閱：17 下載：0
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此篇論文進行了一項尋找希格斯玻色子衰變為一個光子和一個虛光子
的研究。物理分析聚焦於虛光子內部轉換為一對重建質量小於五百億電子
伏特（GeV）的正負電子對。本研究所使用的數據由CMS探測器在LHC上
的質子-質子碰撞中收集。其對撞的中心質心能量為13兆電子伏特（TeV）。
在完整的Run2實驗數據擷取期間，CMS探測器收集到總亮度為為138 fb^{-1} 的數據。事件選擇包含了判定該事件具有來自低質量的虛光子的正負電子對，
隨後在電磁量能器中合併為一個簇射。選擇一個合併的正負電子對和一個
高橫動量的光子是本研究感興趣事件的主要標準。此研究顯示在假設希格
斯玻色子質量為125 GeV的條件下，預測之信號強度上限在95%的信心水
準下為4.78^{+2.23}_{-1.51}倍的標準模型預測且預期的中位數顯著性為0.41個標準差。

A search is conducted for the decay of a Higgs boson into a real and a virtual photon. In this analysis, particular attention is given to the internal conversion of the virtual photon into an electron pair with an invariant mass mee < 50 GeV. The data utilized for this study was recorded by the CMS experiment at the LHC from proton-proton collisions with a center-of-mass energy of 13 TeV during the full Run2 period, corresponding to an integrated luminosity of 138 fb^{−1}. The selection involves identifying events that exhibit a collimated electron pair originating
from a low-mass \gamma^*, which subsequently merges into a single cluster at the electro-magnetic calorimeter. This merged electron, along with a high momentum photon, are the primary criteria for selecting events of interest. The expected limit at 95% conﬁdence level (CL) on the signal strength is estimated to be 4.78+2.23−1.51 times the prediction of the Standard Model (SM) by assuming the mass of the Higgs boson
is 125 GeV. Additionally, the median expected signiﬁcance at mH = 125 GeV is determined to be 0.41\sigma.

Introduction 1
1 StandardModel............................... 1
2 Higgsmechanism.............................. 5
3 Higgsproductionsanddecays ...................... 10
4 TherareHiggsdecayH→γ∗γ→eeγ.................. 13
4.1 Overview .............................. 13 1.4.2 Featuresofthedecay........................ 15 1.4.3 Background composition ..................... 16 1.4.4 PreviousresultsfromATLASandCMS . . . . . . . . . . . . . 18
Experimental apparatus 19

1 LargeHadronCollider ........................... 19 2.2 CompactMuonSolenoid.......................... 20
Analysis procedures 23
1 Dataandsimulatedsamples........................ 23 3.1.1 Datasample............................. 23 3.1.2 Simulatedsamples ......................... 23
2 Trigger .................................... 27 3.2.1 ThechoiceoftheHLT ....................... 28 3.2.2 HLTefficiencymeasurements................... 29
3 Objectreconstructionandidentification . . . . . . . . . . . . . . . . . 36 3.3.1 Electron ............................... 36
3.2 Photon................................ 64
3.3 Jets.................................. 68
4 Eventselection................................ 71
5 Eventcategorization ............................ 71
6 Backgroundandsignalmodelings .................... 75
6.1 Nonresonantbackgroundmodeling ............... 75
6.2 Signalmodeling........................... 79
7 Uncertainties................................. 88 3.7.1 Theoreticaluncertainties...................... 88 3.7.2 Signalnormalizationuncertainties . . . . . . . . . . . . . . . . 88 3.7.3 Signalshapeuncertainties..................... 90 3.7.4 Backgroundshapeuncertainties ................. 90
Results 91
1 Asymptoticlimitandsignificance..................... 91 4.2 Future plans................................. 93 4.3 Conclusions ................................. 94
A Input features of merged MVA ID 95
A.1 ECALBarrel................................. 95 A.2 ECALEndcap................................ 99
B Signal modelings Bibliography
109
                                

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