以大型強子對撞機裡的緊湊渺子線圈偵測器尋找重夸克在半輕子頻道衰變成頂夸克和光子

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研究生：	張祐祥 Yu-hsiang Chang
論文名稱：	以大型強子對撞機裡的緊湊渺子線圈偵測器尋找重夸克在半輕子頻道衰變成頂夸克和光子 Search for pair production of a heavy quark decaying into top quark and photon in semi-leptonic channel with the CMS detector in the LHC
指導教授：	余欣珊 Shin-Shan 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：	2014
畢業學年度：	102
語文別：	英文
論文頁數：	94
中文關鍵詞：	重夸克、緊湊渺子線圈、大型強子對撞機、頂夸克、光子
外文關鍵詞：	heavy quark, CMS, LHC, top quark, photon
相關次數：	點閱：21 下載：0
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我們使用CMS在2012年所蒐集的積分亮度為19.7-1 fb、LHC質子對撞質心能量為8 TeV的數據來找尋激發態頂夸克。在我們分析中的衰變過程和最終產物是：激發態頂夸克、反激發態頂夸克->頂夸克、光子、反頂夸克、光子->底夸克、W玻色子、光子、反底夸克、W玻色子、光子，然後其中一個W玻色子以輕子的方式衰變而另一個W玻色子以夸克的方式衰變，所以我們藉著要求事件中有兩個光子、一個輕子和至少四個噴流來定義訊號區域。χ2排序法被用來重建激發態頂夸克的質量，並且從數據中有十二個事件在訊號區域被觀察到。矩陣法被用在兩個光子的頻道裡來估計這十二個事件中的背景貢獻。這個研究的結果是沒有顯著的超過預期的多餘事件被觀察到，所以對於激發態頂夸克的質量我們以95%的信心水準設了一個低限在969 GeV/c2。

Using the data collected by the CMS detector in 2012, corresponding to a luminosity of 19.7 / fb of proton-proton collisions at LHC center-of-mass energy of 8 TeV, we search for the excited top quark, T*. The decay process and the final states studied in our analysis are: T* T*bar -> t γ tbar γ -> b W+ γ bbar W- γ, where one W boson decays hadronically and the other leptonically, so we define a signal region by requesting events with 2 photons, 1 lepton and >= 4jets. To reconstruct the invariant mass of T*, a χ2-sorting method is used and 12 events are observed in the signal region from data. The matrix method is used to estimate the background contribution among the observed 12 events in the di-photon channel. As a result of this study, no significant excess is observed over expectations and a lower limit is set on a t* quark mass of 969 GeV/c2 at 95% confidence level.

Contents
Abstract ……………………………………………………………… i
中文提要 ……………………………………………………………… ii
感謝 ……………………………………………………………… iii
Contents ……………………………………………………………… iv
List of table ……………………………………………………………… v
List of figure ……………………………………………………………… vi

Chapter 1 Introduction   1
Chapter 2 LHC and CMS detector    3
2.1 The Large Hadron Collider   3
2.2 The Compact Muon Solenoid Detector  5
2.2.1 Tracker  6
2.2.2 Electromagnetic Calorimeter    9
2.2.3 Hadronic Calorimeter   10
2.2.4 Muon Chamber   12
2.2.5 Magnet system    13
Chapter 3 CMS Trigger  14
3.1 Level-1 trigger    15
3.1.1 Muon triggers system in L1  17
3.1.2 Calorimeter triggers system in L1   17
3.1.2.1 The Electromagnetic Candidate Algorithm   19
3.1.2.2 The Jet Candidate Algorithm    21
3.1.2.3 Other calorimeter trigger tasks   23
3.1.3 Global trigger in L1    24
3.2 High Level trigger    25
3.2.1 electrons/photons    25
3.2.2 Muon    35
3.2.3 Jet     36
3.2.4 Missing transverse energy    37
3.3 The triggers used in our analysis     38
Chapter 4 Event reconstruction in offline and our event selection    39
4.1 The anti-kt jet algorithm      39
4.2 The particle flow (PF) algorithm     41
4.3 The r9 variable and the missing hits    43
4.4 The shower shape variable σiηiη     44
4.5 The isolation variables      45
4.6 The event selection in our analysis      46
Chapter 5 data and the simulated sample    51
Chapter 6 Mass Reconstruction    60
6.1 The χ2-sorting method    60
6.2 The neutrino’s pz solution    62
Chapter 7 background estimation: the matrix method   63
7.1 The introduction of matrix method   63
7.2 the photon fake rate from lepton εl    66
7.3 The photon fake rate from jet εj       68
7.4 The photon signal efficiency εs         72
7.5 The ratio factor       74
Chapter 8 Result      75
Chapter 9 Conclusion     79
Appendix A the derivation of Matrix method   80
Reference    90

List of tables
Table 3.1 the list of the objects sent from GCT to GT   18
Table 3.2 tau decay branching ratio 22
Table 3.3 global trigger menu   24
Table 3.4 parameter of hybrid algorithm   28
Table 3.5 trigger path of our analysis   38
Table 5.1 dataset of our analysis  51
Table 5.2 MC samples used in our analysis   52
Table 5.3 event yields before/after scale factors  53
Table 5.4 event yields in the loose region  59
Table 7.1 fit result of fake rate from jets   71
Table 8.1 event yields in the signal region    77

List of figures
Figure 1.1 The diagram of t* decay   2
Figure 2.1 The CERN accelerator complex  3
Figure 2.2 The main accelerator rings and their beam particles   4
Figure 2.3 The CMS detector          5
Figure 2.4 The CMS coordinate     6
Figure 2.5 The pixel detector      6
Figure 2.6 The pixel material budget    7
Figure 2.7 The layout of tracker     8
Figure 2.8 The layout of tracker     9
Figure 2.9 The layout of ECAL     10
Figure 2.10 The relative positions of ECAL and HCAL     11
Figure 2.11 The relative positions of muon chambers    13
Figure 3.1 The overview of the L1-trigger and the HLT     15
Figure 3.2 the schematic diagram of the data flow in L1-trigger    16
Figure 3.3 the L1-trigger   16
Figure 3.4 The strip, the trigger tower and the calorimeter region grouping   18
Figure 3.5 illustration of the calorimeter trigger e/γ algorithm    20
Figure 3.6 illustration of the calorimeter trigger jet algorithm    22
Figure 3.7 Illustration of the Island clustering algorithm      26
Figure 3.8 Illustration of the super-clusters       27
Figure 3.9 Domino construction step of Hybrid algorithm     27
Figure 3.10 Illustration of the crystal off-pointing and the schematic diagram    30
Figure 3.11 Distribution of Emeas/Etrue            31
Figure 3.12 Emeas/Etrue as a function of the number of crystals     32
Figure 3.13 matching the hits in pixel detector      33
Figure 4.1 anti-kt clustered jets          40
Figure 4.2 consideration of the Bremsstrahlung photon emission of electron     42
Figure 4.3 The schematic diagram of particle flow algorithm         43
Figure 4.4 Missing Hits          44
Figure 4.5 Sketch of the photon isolation        45
Figure 5.1 The number of vertices before/after applying scale factors       54
Figure 5.2 the objects’ multiplicities       55
Figure 5.3 the kinematic distributions      56
Figure 5.4 Four leading jets pT distributions      57
Figure 5.5 Jets’ pT distributions for run dependences    58
Figure 6.1 The invariant mass of a top and a photon using the χ2-sorting method   61
Figure 6.2 The t* mass spectra with different neutrino’s solutions    62
Figure 7.1 the schematic of 3 levels of the events with two photons    64
Figure 7.2 the schematic of the tight, the loose and the FO selection of photon   64
Figure 7.3 Electron-Photon invariant mass fit for the no-electron-veto selection and the tight ID selection     67
Figure 7.4 the object has a photon associated with a jet within the cone of size 0.5   68
Figure 7.5 the schematic of the NjFO and NjT       69
Figure 7.6 Results of the template fitting for the various categories    71
Figure 7.7 Muon-Muon-Photon invariant mass fit for the no-electron-veto selection and the tight ID selection   73
Figure 8.2 The mass spectrum in the signal region    76
Figure 8.3 the exclusion limit   78
Figure A-1    82
Figure A-2  83
Figure A-3   86
Figure A-4  87

                                

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