在緊湊渺子線的質心對撞能量為 13 兆電子伏特的數據裡, 用字母法輔以突起搜尋之方法來尋找類 Z 玻色子衰變為 Z 玻色子及希格斯粒子在衰變為輕子與底垮克

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研究生：	張祐祥 Yu-Hsiang Chang
論文名稱：	在緊湊渺子線的質心對撞能量為 13 兆電子伏特的數據裡, 用字母法輔以突起搜尋之方法來尋找類 Z 玻色子衰變為 Z 玻色子及希格斯粒子在衰變為輕子與底垮克 Using Alphabet Assisted Bump Hunt to Search for Z' to Zh to ll bb at sqrt(s)=13 TeV with the CMS Detector
指導教授：	余欣珊 Shin-Shan Yu
口試委員:
學位類別：	博士 Doctor
系所名稱：	理學院 - 物理學系 Department of Physics
論文出版年：	2019
畢業學年度：	107
語文別：	英文
論文頁數：	99
中文關鍵詞：	底垮克、緊湊秒子線圈、大型強子對撞機
外文關鍵詞：	b-tagging
相關次數：	點閱：26 下載：0
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用 2016 年在緊湊秒子線圈從質心對撞能量為 13 兆電子伏特的大型強子對撞機的數據來進行一個對類 Z 新粒子的搜尋, 這個數據對應到的積分亮度為 35.8 fb^{-1}。在這個分析中,類 Z 新粒子的衰變頻道是只針對類 Z 新粒子衰變到 Z 玻色子和希格斯粒子來討論,其中希格斯粒子會再衰變為正反底垮克對,而 Z 玻色子則是以輕子頻道來衰變。因為希格斯粒子是被高度地推進,所以兩個底垮克的方向相當平行且被重建在一個半徑為 0.8 的胖噴流裡。雙底垮克標記演算法和希格斯粒子質量區間的要求是被施加來減少背景事件。剩下的背景事件是由字母法輔以突起搜尋之方法來估計。字母法是用來估計在信號區域的事件數,而信號區域和控制區域的同步擬合用來決定形狀。

A search for a new particle Z’ is performed in the data collected by the CMS detector in 2016 at the LHC center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 35.8 fb^{-1}. The decay channel of Z’ is focused on Z’ to Z H, and the Higgs boson decays to b bar while the Z boson decays leptonically. Since the Higgs boson is highly boosted, the two b-quarks are collimated and thus reconstructed in a fat jet with a radius of 0.8. The double-b tagger algorithm and the Higgs mass window cut are applied to reduce the background events. The remaining background events are estimated by the ALPHABET assisted Bump Hunt method, where the ALPHABET method constraints the event yields in the signal region, and the simultaneous fit in both the signal region and the control region determines the shape.

Introduction 1

1 TheoryMotivation ........................... 1 

2 AnalysisStrategy ............................ 4

The Experimental Setup 5

1  LargeHadronCollider ......................... 5

2  CompactMuonSolenoid........................ 5

2.1  Tracker.............................. 7

2.2  ElectromagneticCalorimeter ................. 7

2.3  HadronicCalorimeter ..................... 8

2.4  Magnet.............................. 9

2.5  MuonSystem .......................... 10

Datasets and Simulation Samples 11

1  Data.................................... 11

2  Trigger .................................. 12

3  MonteCarlosample .......................... 15

3.1 Signal............................... 15 

3.2 Background ........................... 16

Event Selection 19

1 VertexandPileUp............................ 19 

2 Electrons................................. 19 

3 Muons .................................. 21 

4 Jets .................................... 22 

5 JetMass.................................. 23 

6 b-Tagging................................. 24 

7 FinalSelection.............................. 25

Data MC comparison 29

Background Estimation 37

1 Alphabet................................. 37

2 AlphabetAssistedBumpHunt(AABH) ............... 45 

2.1 Alphabet............................. 45 

2.2 Methodvalidation ....................... 47 

2.3 BumpHunt ........................... 49 

2.4 Signalmodeling......................... 50 

2.5 ZHmodeling .......................... 53 

2.6 simultaneousfit......................... 54

Systematic Uncertainties 57

1 Pile-up .................................. 58 

2 Double-btagger............................. 58 

3 HiggsMassTagging .......................... 58 

4 JetEnergyScaleandResolution.................... 59 

5 JetmassScaleandResolution ..................... 59 

6 Trigger .................................. 60 

7 LeptonIDandScale........................... 60 

8 QCDscaleandPDF........................... 64 

9 Luminosity................................ 64 

10Pass-FailRatioFit............................ 64 

11SizeoftheControlRegion....................... 65 

12Sizeofthesimulatedsignalsample.................. 66 

13 SummaryoftheSystematicUncertainties . . . . . . . . . . . . . . 66

Result. . . . . . . . . . . . . . 69

Summary. . . . . . . . . . . . . . 73

Bibliography. . . . . . . . . . . . . . 75

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