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研究生： 童宇軒
Henry Tong Yee Shian
論文名稱： Search for heavy resonances decaying into a Z boson and a Higgs boson in the 2l2b final state in pp collisions at √s = 13 TeV
指導教授： 余欣珊
Shin-Shan Eiko Yu
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： 2016
畢業學年度： 105
語文別： 英文
論文頁數： 111
中文關鍵詞： 高能物理 、大強子對撞機 、緊湊渺子線圈偵測器
外文關鍵詞： High Energy Physics, Large Hadron Collider, Compact Muon Solenoid
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    • 本篇論文呈現了由新理論模型預測之粒子衰變到一個希格斯粒子和一個 Z 玻色子的分析。本分析使用了於 2015 年由大強子對撞機中的緊湊渺子線圈偵測器所記錄之質子-質子對撞總能量為 13 TeV，總亮度為 2.5 fb-1 的數據。高動量的希格斯粒子衰變到一個底夸克和一個反底夸克，在偵測器裡被偵測為一個大質量的噴流。Z 玻色子有兩個衰變通道，分別為正反電子通道以及正反渺子通道。本分析將分別探討電子通道和渺子通道，各通道將再細分為單底夸克標記和雙底夸克標記此二類別。通過合併電子通道和渺子通道，以及它們所有的底夸克標記類別，結果顯示質量由 800 GeV 至 4000 GeV 的新粒子於 95%信置區間的生產截面上限為 0.063 pb 至0.265 pb。

    A search for heavy resonances decaying to a Higgs boson and a Z boson is presented. The analysis is based on the data collected in 2015 with the CMS detector at a center-of-mass energy √s = 13 TeV, corresponding to an integrated luminosity of 2.51 fb-1. The Higgs bosons are reconstructed from high momentum bb quark pairs that are detected as a single massive jet, while the Z bosons are reconstructed from electron pairs and muon pairs. The analysis is separated in electron and muon channels, with single and double b-tag categories. A 95% upper limit on the production cross section of σX × B(X → ZH) is derived from the combination of four categories with a limit of 0.063 pb to 0.265 pb for mX from 800 to 4000 GeV.

    1 Introduction and Theory Overview 1 1.1 Introduction 1 1.2 Theoretical Motivations 2 1.2.1 Heavy Vector Triplet 3 1.2.2 Explicit Model 7 2 LHC and the CMS Detector 9 2.1 Large Hadron Collider 9 2.2 The Compact Muon Solenoid Detector 11 2.2.1 Magnet System 12 2.2.2 Tracker Detector 13 2.2.3 Electromagnetic Calorimeter 14 2.2.4 Hadron Calorimeter 16 2.2.5 Muon Detector 17 2.3 Trigger System 19 2.3.1 First Level Trigger 20 2.3.2 High Level Trigger 20 3 Analysis Strategy 21 3.1 Data Sets and Monte Carlo Samples 21 3.1.1 Data Sets 21 3.1.2 Monte Carlo Samples 22 3.2 Trigger 23 3.3 Vertex and Pile-up 27 3.4 Physics Objects 28 3.4.1 Electron Reconstruction 28 3.4.2 Electron Selection 30 3.4.3 Muon Reconstruction 32 3.4.4 Muon Selection 33 3.4.5 Jet Reconstruction 35 3.4.6 Jet Selection 40 3.4.7 Boson Reconstruction 40 3.5 Data and Monte Carlo Comparison 40 4 Background Estimation 53 4.1 The Normalization of Z+jets Background 55 4.2 The Shape of Z+jets Background in the mZH Spectrum 56 5 Systematic Uncertainties 71 5.1 Systematics on Background Normalization 71 5.2 Systematics on Background Shape 75 5.3 Systematics on Signal Efficiency 76 5.4 Summary 77 6 Results and Conclusion 81 6.1 Upper Limit on Production Cross Section 81 6.2 Conclusion 85 Bibliography 87

    [1] Vardan Khachatryan et al. “Search for heavy resonances decaying into a vector boson and a Higgs boson in final states with charged leptons, neutrinos, and b quarks”. In: (2016). arXiv: 1610.08066 [hep-ex].
    [2] Peter W. Higgs. “Broken Symmetries and the Masses of Gauge Bosons”. In: Phys. Rev. Lett. 13 (16 Oct. 1964), pp. 508–509. DOI: 10 . 1103 / PhysRevLett . 13 . 508. URL: http : / / link . aps . org / doi / 10 . 1103/PhysRevLett.13.508.
    [3] Georges Aad et al. “Observation of a new particle in the search for the Standard Model Higgs boson with the ATLAS detector at the LHC”. In: Phys. Lett. B716 (2012), pp. 1–29. DOI: 10.1016/j.physletb.2012. 08.020. arXiv: 1207.7214 [hep-ex].
    [4] Serguei Chatrchyan et al. “Observation of a new boson at a mass of 125 GeV with the CMS experiment at the LHC”. In: Phys. Lett. B716 (2012), pp. 30–61. DOI: 10.1016/j.physletb.2012.08.021. arXiv: 1207. 7235 [hep-ex].

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