Exclusive reconstruction of B± in pPb collisions at √sNN = 5.02 TeV
- 주제(키워드) B meson , CMS , pPb collision , B± , open heavy-flavor , quark gluon plasma , cold nuclear matter effect , proton Lead
- 발행기관 고려대학교 대학원
- 지도교수 홍병식
- 발행년도 2015
- 학위수여년월 2015. 8
- 학위구분 박사
- 학과 대학원 물리학과
- 세부전공 원자핵물리학전공
- 원문페이지 146 p
- 실제URI http://www.dcollection.net/handler/korea/000000060667
- 본문언어 영어
- 제출원본 000045841518
초록/요약
In order to diagnose the detailed characteristics of the deconfined partonic matter what are called the quark-gluon plasma (QGP) produced in heavy ion collisions, the heavy quarks are delivered to be useful probes. In particular, the comparison of the energy loss patterns of heavy and light quarks in dense medium will shed some lights on the high-density quantum chromodynamics (QCD), which is yet largely unknown. However it is necessary to understand the cold nuclear matter effect in ground state nuclei beforehand to extract genuine hot and dense matter effect. In this thesis, we present the exclusive reconstruction of B± having been decayed into J/ψ and K±, in pPb collisions at √sNN = 5.02 TeV in CMS at CERN. The J/ψ is reconstructed by opposite-sign muon pair with their decay vertex away from the collision point. From this analysis, the differential cross section of B± is measured as functions of rapidity and transverse momentum. Compared to the FONLL calculations, no significant modification due to the cold nuclear matter effect is found as the nuclear modification factor is consistent with unity within uncertainties.
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1 Introduction 1
2 Theoretical Overview of the analysis 3
2.1 The Standard Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.2 Quantum ChromoDynamics (QCD) . . . . . . . . . . . . . . . . . . . 3
2.3 Quark-Gluon Plasma (QGP) . . . . . . . . . . . . . . . . . . . . . . . 6
2.4 Time evolution from the big bang . . . . . . . . . . . . . . . . . . . . . 8
2.5 Cold nuclear matter effect . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.6 Heavy quark production . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.7 Prediction and discovery of bottom quark . . . . . . . . . . . . . . . . 11
2.8 Heavy quark Decay (flavor transformation) . . . . . . . . . . . . . . . 11
2.9 Summary of the interesting channel . . . . . . . . . . . . . . . . . . . . 12
3 Previous measurement of b-hadron 15
3.1 Binary collision (From UA1 to LHC) . . . . . . . . . . . . . . . . . . . 15
3.2 PbPb collision at √sNN = 2.76 TeV . . . . . . . . . . . . . . . . . . . 16
3.3 pPb collision at √sNN = 5.02 TeV . . . . . . . . . . . . . . . . . . . . 16
4 Large Hadron Collider (LHC) 22
4.1 LHC complex . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
4.2 Useful variables related with LHC . . . . . . . . . . . . . . . . . . . . 23
4.2.1 Center-of-mass energy per nucleon pair . . . . . . . . . . . . . 24
4.2.2 Rapidity boost . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
4.2.3 Relation of rapidity (or pseudo-rapidity) in between Lab. and
center-of-mass frame . . . . . . . . . . . . . . . . . . . . . . . . 25
4.3 Detector systems in LHC . . . . . . . . . . . . . . . . . . . . . . . . . 26
4.3.1 ATLAS (A Toroidal LHC ApparatuS) . . . . . . . . . . . . . . 26
4.3.2 ALICE (A Large Ion Collider Experiment) . . . . . . . . . . . 27
4.3.3 LHCb (Large Hadron Collider beauty) . . . . . . . . . . . . . . 28
5 CMS detector 31
5.1 Particle detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
5.2 Overall CMS detector . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
5.3 Inner tracking system . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
5.4 Electromagnetic calorimeter (ECAL) . . . . . . . . . . . . . . . . . . . 33
5.5 Hadron calorimeter (HCAL) . . . . . . . . . . . . . . . . . . . . . . . . 34
5.6 Muon system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
5.6.1 Drift Tube (DT) . . . . . . . . . . . . . . . . . . . . . . . . . . 35
5.6.2 Cathode Strip Chamber (CSC) . . . . . . . . . . . . . . . . . . 36
6 Resistive Plate Chamber 37
6.1 Overview of the RPC . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
6.2 CMS RPC system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
6.2.1 Summary of the aging test for HLHC . . . . . . . . . . . . . . 39
6.3 General description of the detector . . . . . . . . . . . . . . . . . . . . 39
6.4 Detailed description of parts . . . . . . . . . . . . . . . . . . . . . . . . 42
6.4.1 Electrical shielding, cover plates and sidebars . . . . . . . . . . 42
6.4.2 Gas distribution system . . . . . . . . . . . . . . . . . . . . . . 44
6.4.3 Front-end boards, cables and others . . . . . . . . . . . . . . . 44
6.5 Assembly procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
6.6 Cosmic muon test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
6.7 Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
7 Particle Reconstruction 58
7.1 Track reconstruction . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
7.1.1 Kalman filter technique . . . . . . . . . . . . . . . . . . . . . . 60
7.1.2 Iterative tracking . . . . . . . . . . . . . . . . . . . . . . . . . . 61
7.2 Muon reconstruction . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
8 CMS Trigger System 65
8.1 Muon Level-1 (L1) trigger . . . . . . . . . . . . . . . . . . . . . . . . . 66
8.2 High-Level Trigger (HLT) . . . . . . . . . . . . . . . . . . . . . . . . . 66
9 Analysis of B+ 69
9.1 Datasets and Event Selections . . . . . . . . . . . . . . . . . . . . . . . 69
9.1.1 pPb collisions and Datasets . . . . . . . . . . . . . . . . . . . . 69
9.1.2 Trigger and event selection . . . . . . . . . . . . . . . . . . . . 70
9.2 Prerequisite study with Monte Carlo (MC) . . . . . . . . . . . . . . . 70
9.2.1 Setting for MC sample . . . . . . . . . . . . . . . . . . . . . . . 70
9.3 Particle selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
9.3.1 Muon selection . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
9.3.2 J/ψ candidate reconstruction . . . . . . . . . . . . . . . . . . . 73
9.3.3 Track selection . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
9.3.4 B+ candidate selection . . . . . . . . . . . . . . . . . . . . . . . 74
9.3.5 Signal extraction procedure . . . . . . . . . . . . . . . . . . . . 78
9.3.6 Raw yields of B+ . . . . . . . . . . . . . . . . . . . . . . . . . . 79
9.4 Acceptance and Efficiency . . . . . . . . . . . . . . . . . . . . . . . . . 86
9.4.1 Acceptance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
9.4.2 Efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
9.5 Proton-Proton reference . . . . . . . . . . . . . . . . . . . . . . . . . . 91
9.5.1 Data-driven reference with 7 TeV pp data . . . . . . . . . . . . 91
9.5.2 Summary of the reference study . . . . . . . . . . . . . . . . . 93
9.6 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100
9.6.1 pT -differential cross section in pPb collisions . . . . . . . . . . . 100
9.6.2 Nuclear modification factor RpA of B+ . . . . . . . . . . . . . . 100
9.6.3 Raw yields, pT -differential cross section and nuclear modification
factor RFONLL
pA for B+, B0, and B0
s . . . . . . . . . . . . . 107
9.7 Systematics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
9.7.1 Overall scale related to the cross-section calculation . . . . . . 109
9.7.2 Systematics related to B meson selection, efficiency and acceptance
correction . . . . . . . . . . . . . . . . . . . . . . . . . . 111
9.7.3 Summary of systematics . . . . . . . . . . . . . . . . . . . . . . 116
10 Conclusion 118
Bibliography 119