Study of Zγ-> e+e-γ Process with CMS Detector at Large Hadron Collider

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姓名

吳靖涵(Jing-Han Wu) 查詢紙本館藏

畢業系所

物理學系

論文名稱

(Study of Zγ-> e+e-γ Process with CMS Detector at Large Hadron Collider)

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摘要(中)

本篇論文模擬歐洲大強子對撞機在質心能量為14兆電子伏特高能量的運作下，利用CMS偵測器量測對撞產生Z0γ衰變為e+e-γ的事件。文中所使用的蒙地卡羅數據資料經由事件產生器和CMS套裝軟體完整的模擬實際碰撞情況，其中CMS軟體包含了：模擬粒子與偵測器的作用，以及偵測訊號的數位化處理。我們考慮的大量的背景樣本使模擬條件更接近真實情況。
所選取的事件在CMS偵測器涵蓋範圍內，Z0衰變產生的電子橫向動量需大於10 GeV/c且所選的光子的橫向動量也需大於20 GeV/c。我們量測到在1 fb-1數據資料中230.00個訊號事件以及126個背景事件通過所使用的選擇條件。
其中Z+jets支配了117個背景事件，支配92.86%的背景事件為主要的背景來源。此事件統計上的意義經公式計算得到16.40。
因此，利用大強子對撞機運作初期所產生的0.1 fb-1的實驗數據即可量測統計意義大於5的Z0γ事件。

摘要(英)

We present a simulation of pp?Z0γ process with the e+e-γ final state at using Compact Muon Solenoid detector at Large Hadron Collider. The Monte Carlo samples are fully simulated through the event generator and CMSSW that includes the detector simulation and digitization. In order to achieve realism, we consider a large set of background samples to in this study.
The electrons from Z decay are selected with PTe > 10 GeV/c and the photon is selected with PTγ> 20 GeV/c within the coverage of CMS detector. There are 230 signal events and 126 background events measured after the Zγ selection criteria at 1 fb-1. There are 117 background event form Z+jets process that dominates 92.86 % of the background contribution. The significance is calculated to be 16.40.
As a result, the Z0γ process can be established with the signal statistical sensitivity better than 5σ in the early phase of LHC with the integrated luminosity of 0.1 fb-1.

關鍵字(中)

★ 大強子對撞機

關鍵字(英)

★ LHC
★ CMS

論文目次

1. Introduction-----------------------------------------------------------------------------------1
1.1 The Standard Model---------------------------------------------------------------------1
1.2 Triple Gauge Coupling------------------------------------------------------------------5
1.3 pp Z Production---------------------------------------------------------------------8
1.3.1 Review of Z Measurement at CDF--------------------------------------------- 9
1.3.2 Review of Z Measurement at D0------------------------------------------------9
2. The Experimental Apparatus-------------------------------------------------------------- 10
2.1 The Large Hadron Collider----------------------------------------------------------- 10
2.2 The Compact Muon Solenoid Detector--------------------------------------------- 11
2.2.1 Tracker----------------------------------------------------------------------------- 13
2.2.2 Electromagnetic Calorimeter----------------------------------------------------14
2.2.3 Hadronic Calorimeter-------------------------------------------------------------15
2.2.4 Muon Chamber--------------------------------------------------------------------15
2.2.5 Magnet----------------------------------------------------------------------------- 16
2.3 Triggers and Data Acquisition System----------------------------------------------17
2.3.1 Level-1 Triggers------------------------------------------------------------------ 17
2.3.2 High-Level Triggers--------------------------------------------------------------17
3. CMS Software Components and Simulation--------------------------------------------19
3.1 Simulation Process---------------------------------------------------------------------19
3.1.1 Event Generator-------------------------------------------------------------------19
3.1.2 Geant4 Simulation----------------------------------------------------------------19
3.1.3 Digitization------------------------------------------------------------------------20
3.2 Algorithm of Physical Quantity and Event Filter--------------------------------- 20
3.2.1 Supercluster Algorithm in the ECAL------------------------------------------20
3.2.2 Position Measurement in the ECAL-------------------------------------------- 21
3.2.3 Event Filter------------------------------------------------------------------------- 22
3.3 Objects Reconstruction--------------------------------------------------------------- 23
3.3.1 Electron Reconstruction--------------------------------------------------------- 23
3.3.2 Photon Reconstruction-----------------------------------------------------------24
3.3.3 Muon Reconstruction------------------------------------------------------------ 25
3.3.4 Jet Reconstruction---------------------------------------------------------------- 25
3.3.5 Missing ET Reconstruction------------------------------------------------------26
3.4 Signal and Background Datasets---------------------------------------------------- 26
3.4.1 The Signal Datasets---------------------------------------------------------------26
3.4.2 The Background Datasets--------------------------------------------------------29
3.4.3 The Calculation of the Expected Event Yield--------------------------------- 34
4. Data Analysis--------------------------------------------------------------------------------39
4.1 Electron Selection Criteria------------------------------------------------------------ 39
4.1.1 Electron Identification------------------------------------------------------------ 40
4.1.2 Electron Reconstructed Efficiency----------------------------------------------43
4.2 Z Boson Selection Criteria------------------------------------------------------------ 45
4.2.1 Z Boson Event Selection--------------------------------------------------------- 45
4.2.2 Z Boson Reconstructed Efficiency---------------------------------------------- 46
4.3 Photon Selection Criteria-------------------------------------------------------------- 48
4.3.1 Photon Identification------------------------------------------------------------- 48
4.3.2 Photon Reconstructed Efficiency----------------------------------------------- 49
4.4 Z0 Event Selection Criteria----------------------------------------------------------- 52
4.4.1 Z0 Selection-------------------------------------------------------------------------- 52
4.4.2 Z0 Selection Efficiency---------------------------------------------------------- 53
4.5 The Event Yields of Signal and Backgrounds-------------------------------------- 54
4.6 The Main Background----------------------------------------------------------------- 61
4.7 Systematic Uncertainties-------------------------------------------------------------- 63
4.8 Result------------------------------------------------------------------------------------ 64
5. Summary------------------------------------------------------------------------------------- 67
Reference--------------------------------------------------------------------------------------- 68
Appedix----------------------------------------------------------------------------------------- 70

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指導教授

張元翰(Yuan-Hann Chang)

審核日期

2009-7-17

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