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Searching for heavy neutrinos using the LHC proton-proton collision data at sqrt(s) = 13 TeV collected by the CMS detector : CMS 검출기로 수집된 거대 강입자 충돌기의 질량중심 에너지 13 TeV 양성자-양성자 충돌 데이터를 사용한 무거운 중성미자 탐사
| DC Field | Value | Language |
|---|---|---|
| dc.contributor.advisor | 양운기 | - |
| dc.contributor.author | 오성빈 | - |
| dc.date.accessioned | 2022-04-20T07:51:29Z | - |
| dc.date.available | 2022-04-20T07:51:29Z | - |
| dc.date.issued | 2021 | - |
| dc.identifier.other | 000000167458 | - |
| dc.identifier.uri | https://hdl.handle.net/10371/178946 | - |
| dc.identifier.uri | https://dcollection.snu.ac.kr/common/orgView/000000167458 | ko_KR |
| dc.description | 학위논문(박사) -- 서울대학교대학원 : 자연과학대학 물리·천문학부, 2021.8. 양운기. | - |
| dc.description.abstract | Among several unveiled key questions about the universe, neutrinos masses and its mechanism are clear evidence beyond the Standard Model (SM). In addition, unique chiral structure of the weak interaction of the SM is unnatural in the sense of parity violation without certain source of it. The left-right symmetric extension of the SM is traditional way to explain the parity violation with specific Higgs sector, for example, a bi-doublet and two triplets, which takes the see-saw mechanism into the model in natural way that can explain the smallness of neutrino masses. The models SU(2)L X SU(2)R X U(1)B-L group is reduced to the group identical to the SM, SU(2)L X U(1)Y, by spontaneous symmetry breaking (SSB) of Higgs sector, and, once again to U(1)em also by SSB.
In this thesis, the search for pair production of heavy neutrinos via the decay of new neutral gauge boson (Z') in the proton-proton collisions at sqrt(s) = 13TeV in same flavor di-lepton (e or μ) plus at least two jets channel is presented. The data set corresponds to the integrated luminosity of 137.4 /fb collected by the Compact Muon Solenoid (CMS) detector at the Large Hadron Collider (LHC). | - |
| dc.description.abstract | 입자물리학은 20세기를 거쳐 눈부신 발전을 이뤄냈지만 여전히 이 우주에는 밝혀지지 않은 수수께끼들이 있다. 그 중에서도 중성미자의 질량과 그것을 생성하는 기작은 표준모형을 넘어서는 이론이 필요하다고 주장하는 대표적인 현상 중 하나다. 이에 덧붙여서, 약한상호작용이 가지는 특이한 카이랄성은 반전성 대칭 붕괴에 대해 확실한 근거를 제공하지 못한다는 점에서 자연스럽지 않다. 표준모형의 좌우대칭 확장은 이러한 문제를 해결하는 전통적인 방법 중 하나다. 여기에 다소 복잡한 힉스보존 구조를 사용하면, 예를들어 하나의 겹이중항과 두개의 삼중항, 중성미자 질량이 다른 페르미 입자들보다 왜 크게 작은지 설명할 수 있는 시소(see-saw)기작이 자연스럽게 적용된다. 이 확장된 모형의 군은 SU(2)L X SU(2)R X U(1)B - L 로 표현되며, 자발적 대칭성 붕괴를 통해 낮은 에너지 수준에서는 표준모형과 동일한 SU(2)L X U(1)Y 군으로 근사된다. 여기서 한번더 자발적 대칭성 붕괴에 의해 U(1)em 군으로 표현된다.
이 논문에서는 질량중심 에너지 13 TeV 으로 발생시킨 양성자-양성자 충돌에서 위 모형에서 등장하는 새로운 중성 게이지 보존 (Z')이 생성되고, 이것이 두개의 무거운 중성미자로 붕괴하는 반응을 탐사한 결과를 발표한다. 이 과정에서 두개의 하전 경입자와 네개의 젯들이 형성되는데, 하전 경입자들의 경우 두개의 전자 혹은 두개의 뮤온이 생성되는 과정만 고려되었다. 분석에 사용한 데이터는 거대 강입자 가속기에 있는 CMS 검출기로 수집하였으며, 총 137.4 /fb 의 총 적분 광도량에 해당한다. | - |
| dc.description.tableofcontents | Chapter 1 Introduction 1
Chapter 2 Theoretical Background 5 2.1 TheStandardModel(SM) 13 2.2 The left-right Symmetric Extension of the SM 41 Chapter 3 LHC 57 3.1 The LHC Injection Chain 60 3.2 Magnets 64 3.3 Radio Frequency(RF) Cavity 68 Chapter 4 The CMS Detector 73 4.1 Structure of the CMS 74 4.1.1 Concept of Silicon (semiconductor) Tracker 76 4.1.2 Concept of the Crystal ECAL 78 4.1.3 Concept of the HCAL 80 4.1.4 The Superconducting Solenoid and Iron Yoke 82 4.1.5 Concept of Gaseous Trackers and the Muon System of the CMS 84 4.2 Triggering 86 4.2.1 The Level1 Trigger 87 4.2.2 The High Level Trigger 91 4.3 Particle Reconstruction, the Particle Flow Algorithm 92 Chapter 5 Monte Carlo Samples 96 5.1 Monte Carlo (MC) Simulation 96 5.2 Monte Carlo Samples 101 5.2.1 Signal sample generation 101 5.2.2 Background samples 104 Chapter 6 Data Samples 107 6.1 Overview 107 6.2 Triggers 108 6.2.1 Signal kinematics 108 6.2.2 Trigger lists 114 Chapter 7 Objects and Event Selection 115 7.1 Objects 115 7.1.1 Primary vertex selection 115 7.1.2 Jet reconstruction 116 7.1.3 Jet selection 117 7.1.4 Mass of AK8 jets 117 7.1.5 Electron selection 119 7.1.6 Muon selection 123 7.2 Event Selection 125 7.2.1 Jet selection priority 125 7.2.2 Three orthogonal number of jets bins 125 7.2.3 Signal region 129 7.2.4 Expected Background and Signal Shape 129 Chapter 8 Selection efficiency 131 Chapter 9 Corrections 135 9.1 Jet energy correction 135 9.1.1 L1 Pileup 135 9.1.2 L2L3 MC truth correction 137 9.1.3 L2L3 Residual correction 138 9.2 Pileup correction 139 9.3 Lepton energy/momentum correction 140 9.3.1 Electrons 140 9.3.2 Muons 142 9.4 Lepton identification and trigger efficiency corrections 147 9.4.1 The tag-and-probe method 147 9.5 Level1e/gamma trigger prefiring correction 149 9.6 Consideration on HEM 15/16 issue of the CMS detector 152 Chapter 10 Background Estimation 162 10.1 DY+Jets background estimation 163 10.2 Top quark background estimation 176 10.3 Normalization Factor Fitting Results 176 10.4 Checking the level of expected contributions from non-prompt leptons and charge-flip 176 10.4.1 Expected background level of charge miss-identified electrons 176 10.4.2 Expected background level from non-prompt leptons 182 10.4.3 Conclusion for Same-sign Background 184 Chapter 11 Systematic Uncertainties 186 11.1 Experimental sources of uncertainties 186 11.2 Systematic uncertainties from statistical sources 188 11.3 Prefit and postfit reconstructed Z prime mass plots in CRs 190 Chapter 12 Results 194 Chapter 13 Conclusions 200 Appendix A Reasons of charge blinded analysis on dilepton 210 A.1 Small statistics at highest signal region bin 210 A.2 Difficulty on nonprompt lepton background modeling 213 A.3 Charge mismeasurement of electrons 214 A.4 Two main background of SS region should be measured using MC simulation, and they are detector condition based backgrounds 214 Appendix B Why b-veto cut is not applied 215 Appendix C Limit plots for all mass points 218 C.1 Dimuon channel 218 C.2 Dielectron channel 221 Appendix D Signal Injection Test 223 Appendix E Comparing result with ATLAS 8 TeV analysis 226 Appendix F Control region plots for each number of fatjets bin 228 F.1 2016Campaign 228 F.2 2017Campaign 247 F.3 2018Campaign 265 Appendix G Comparison between private and official signal samples 283 Appendix H Events in the highest bin of 2AK8 ee SR 287 H.1 Event display of 2016, 1st event 288 H.2 Event display of 2017, 1st event 290 H.3 Event display of 2017, 2nd event 291 H.4 Event display of 2017, 3rd event 292 H.5 Event display of 2017, 4th event 293 H.6 Event display of 2018, 1st event 294 H.7 Event display of 2018, 2nd event 295 H.8 Event display of 2018, 3rd event 296 H.9 Event display of 2018, 4th event 297 Appendix I Events in the 1500 to 1800 GeV bin of 2AK8 mumu SR 298 I.1 Investigations on second muon pT 307 I.2 Investigations on energy fractions of AK8 jets and angular distribution between AK8 jets and muons 310 I.3 Reconstructed Z prime mass distributions using tight muons 317 I.4 Conclusion of investigation 319 Appendix J Interpretations on 1D cross section limits 320 J.1 Dielectron channel 320 J.2 Dimuon channel 320 초록 325 Acknowledgements 326 | - |
| dc.format.extent | xxxiv, 327 | - |
| dc.language.iso | eng | - |
| dc.publisher | 서울대학교 대학원 | - |
| dc.subject | SNU | - |
| dc.subject | High energy physics | - |
| dc.subject | Thesis | - |
| dc.subject | 서울대학교 | - |
| dc.subject | 고에너지물리학 | - |
| dc.subject | 졸업논문 | - |
| dc.subject.ddc | 523.01 | - |
| dc.title | Searching for heavy neutrinos using the LHC proton-proton collision data at sqrt(s) = 13 TeV collected by the CMS detector | - |
| dc.title.alternative | CMS 검출기로 수집된 거대 강입자 충돌기의 질량중심 에너지 13 TeV 양성자-양성자 충돌 데이터를 사용한 무거운 중성미자 탐사 | - |
| dc.type | Thesis | - |
| dc.type | Dissertation | - |
| dc.contributor.AlternativeAuthor | Sungbin Oh | - |
| dc.contributor.department | 자연과학대학 물리·천문학부 | - |
| dc.description.degree | 박사 | - |
| dc.date.awarded | 2021-08 | - |
| dc.contributor.major | 입자물리학 실험 | - |
| dc.identifier.uci | I804:11032-000000167458 | - |
| dc.identifier.holdings | 000000000046▲000000000053▲000000167458▲ | - |
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