Title Page
Abstract
Contents
Chapter 1. Preface 20
Chapter 2. Theoretical Backgrounds 25
2.1. The Standard Model of Particle Physics 25
2.1.1. Elementary Particles and Fundamental Forces 25
2.1.2. Open Issues with the Standard Model 29
2.2. Monte-Carlo Event Simulation 30
2.2.1. Factorization Theorem 30
2.2.2. Parton Distribution Function 31
2.2.3. Hard Process 33
2.2.4. Parton Shower and Hadronization 35
2.2.5. Detector Simulation 38
2.2.6. Pileup Events 39
Chapter 3. Experimental Backgrounds 41
3.1. The Large Hadron Collider (LHC) 41
3.1.1. Luminosity 44
3.2. The Compact Muon Solenoid (CMS) Detector 46
3.2.1. Coordinate System 46
3.2.2. Tracking System 48
3.2.3. Electromagnetic Calorimeter 49
3.2.4. Hadronic Calorimeter 51
3.2.5. Muon System 53
3.2.6. Data Acquisition 55
3.3. Particle-Flow Algorithm : Event Reconstruction 56
3.3.1. Tracks and Primary Vertex 57
3.3.2. Muons 59
3.3.3. Electrons and Photons 60
3.3.4. Jets 61
3.3.5. Taus 63
Chapter 4. Neutrinos 64
4.1. History of Neutrinos 64
4.1.1. Radioactive Beta Decay 64
4.1.2. A Desperate Remedy 66
4.1.3. Observation of Neutrinos 67
4.1.4. Solar Neutrinos 69
4.2. Neutrino Mass Models 71
4.2.1. Type-I Seesaw Model 72
4.2.2. Type-II Seesaw Model 74
4.2.3. Left-Right Symmetric Model 75
4.3. Search for Heavy Neutrinos at the CMS 75
4.3.1. Type-I Seesaw Model in Dilepton Channel at 8 TeV 76
4.3.2. Left-Right Symmetric Model in Dilepton Channel at 8 TeV 76
4.3.3. Composite Model in Dilepton Channel at 13 TeV 79
4.3.4. Type-I Seesaw Model in Dilepton Channel at 13 TeV 81
4.3.5. Left-Right Symmetric Model in Dilepton Channel at 13 TeV 83
4.3.6. Overall Review and Outlook 85
Chapter 5. Search for Heavy Neutrino at the CMS 86
5.1. Introduction 86
5.2. CMS Dataset and Triggers 88
5.2.1. Data 88
5.2.2. MC Event Samples 88
5.2.3. Trigger Selection 96
5.3. Object Definition 96
5.3.1. Leptons : Electron and Muon 96
5.3.2. Jets : AK4 and AK8 Jets 99
5.3.3. Missing Transverse Momentum 102
5.4. Analysis Strategy 103
5.4.1. Background Estimation 103
5.4.2. Signal Process Event Kinematics 103
5.4.3. Preselection 104
5.4.4. Signal Region 107
5.4.5. Control Region 118
5.5. Systematic Uncertainties 120
5.5.1. Systematic Uncertainties from Objects 121
5.5.2. Systematic Uncertainties from Detector Effects 124
5.5.3. Systematic Uncertainties from Theoretical Effects 125
5.6. Results 126
5.6.1. Effective Transverse Mass Distributions 126
5.6.2. Statistical Method 134
5.6.3. Interpretation 135
5.6.4. Summary 136
Chapter 6. Neutrino Mass Model Reinterpretations with Published LHC Results 141
6.1. Reinterpretation 141
6.1.1. Tools for Reinterpretation 146
6.1.2. Constraints on New Theories Using RIVET (CONTUR) 149
6.2. Reinterpretation with Published LHC Results 152
6.2.1. Type-I Seesaw Model 152
6.2.2. Type-II Seesaw Model 156
6.3. Results 166
Chapter 7. Conclusions 169
7.1. Summary 169
7.2. Outlook 170
Bibliography 173
Abstract 189
Table 2.1. Properties of the fermions in the SM. 26
Table 2.2. Properties of the bosons in the SM. 27
Table 5.1. Name of triggers used for the analysis. 97
Table 5.2. Sources of systematic uncertainties and its year-by-year correlation treatments. 121
Figure 1.1. Image depicting the substructures of matter ending with the elementary level, quarks. Figure credit : CERN. 21
Figure 1.2. 59 hadrons discovered since 2011 by the Large Hadron Collider until the May of 2021. Figure credit : CERN. 21
Figure 2.1. PDF at NNLO is shown as an example at factorization scales of 10 GeV² (left) and 10⁴ GeV² (right) extracted from NNPDF collaboration.[이미지참조] 33
Figure 2.2. The quark potential from quenched lattice QCD shown in lattice units (0.1 fm). 37
Figure 2.3. Example figures of jet merging scales. Left and right depicts the case where jet merging scale (cutoff) is chosen either too low or too high inducing... 39
Figure 2.4. An event collected by CMS in 2015, Run/Event number 195099/35438125 showing the reconstructed vertices. Figure credit : CMS. 40
Figure 3.1. The accelerator complex of CERN in 2022. Smaller machines form a chain to boost the particles before being injected to LHC beam pipe. Figure... 42
Figure 3.2. Cumulative luminosity versus day delivered to CMS for collisions at nominal center-of-mass energy. Figure credit : CMS. 45
Figure 3.3. 3D overview of the CMS detector showing layers of components. Figure credit : CERN. 47
Figure 3.4. The coordinate system of CMS detector. Figure Credit : Izaak Neutelings. 48
Figure 3.5. The tracking system of CMS detector. It is separated into multiple parts, including the pixel part in the center (PIXEL), tracker inner barrel... 50
Figure 3.6. Schematic view of the CMS ECAL system. 51
Figure 3.7. Schematic view of the CMS HCAL system. 52
Figure 3.8. Schematic view of the CMS muon system. DT, CSC, and RPC are colored in green, blue, red, respectively. 54
Figure 3.9. Depiction of the data processing flow of the CMS experiment. Among 40 M events occuring per second, about a thousand events are selected by the... 56
Figure 3.10. The sketch of a specific particle's interactions as it propagates through the CMS detector starting from the interaction point. Cyan, red, and... 58
Figure 3.11. An illustrative diagram of the four main jet reconstruction algorithms. The jet reconstructions are performed on the same data with same... 61
Figure 4.1. Beta decay spectrum measured by Ellis and Wooster from bismuth-210 using calorimeter. 66
Figure 4.2. The letter from Pauli. 68
Figure 4.3. Weinberg operator and its opening to three different seesaw models. 72
Figure 4.4. Exclusion limits set on mN - |VNℓ|2 parameter space. From left to right shows the mixing limits set from dimuon, dielectron, and electron-muon channels.[이미지참조] 77
Figure 4.5. Exclusion limits set on mWR - mN parameter space. Left and right each shows the exclusion limits set from dimuon and dielectron channels, respectively.[이미지참조] 78
Figure 4.6. Exclusion limits set on mWR - mN parameter space. Left and right shows the exclusion limits set from dimuon and dielectron channels, respectively.[이미지참조] 79
Figure 4.7. Distribution of m(ℓℓjj) for (mWR, mN)=(2.5, 1.25) TeV scenario. Left and right shows the distributions from dimuon and dielectron channels, respectively.[이미지참조] 80
Figure 4.8. Exclusion limits set on mN - Λ parameter space. Left and right shows the exclusion limits set from dimuon and dielectron channels, respectively.[이미지참조] 81
Figure 4.9. Feynman diagrams of type-I seesaw model's same-sign dilepton channel. Left is the typical charged current DY channel and right is the γ induced... 82
Figure 4.10. Exclusion limits set on mN - |VNℓ|2 parameter space. From left to right shows the mixing limits set from dimuon, dielectron, and electron-muon channels.[이미지참조] 83
Figure 4.11. Exclusion limits set on mWR - mN parameter space. Left and right each shows the exclusion limits set from dimuon and dielectron channels, respectively.[이미지참조] 84
Figure 4.12. Exclusion limits set on mWR - mN parameter space. Left and right each shows the exclusion limits set from dimuon and dielectron channels, respectively.[이미지참조] 84
Figure 5.1. Heavy N Feynman diagrams with single lepton final state in particle level. 87
Figure 5.2. On the left is the NLO cross sections for CC DY, NC DY, and γ induced VBF processes with single lepton final state. Lower panel shows the... 93
Figure 5.3. ParticleNet score distributions for Xbb (left) and Xqq (right) after preselection. 102
Figure 5.4. pT (left) and η (right) distributions of leptons in signal processes.[이미지참조] 104
Figure 5.5. △R(bb) and pT(Xgen) distributions in signal processes.[이미지참조] 105
Figure 5.6. Transverse momentum of the lepton distributions for full Run 2 after preselection. The distributions are separately shown for electron merged (top... 108
Figure 5.7. Pseudorapidity of the lepton distributions for full Run 2 after preselection. The distributions are separately shown for electron merged (top left),... 109
Figure 5.8. Number of jet distributions for full Run 2 after preselection. The distributions are separately shown for electron merged (top left), resolved (top... 110
Figure 5.9. Number of b-tagged jet distributions for full Run 2 after preselection. The distributions are separately shown for electron merged (top left), resolved... 111
Figure 5.10. Missing transverse energy distributions for full Run 2 after preselection. The distributions are separately shown for electron merged (top left),... 112
Figure 5.11. Reconstructed mass of boson from N decay distributions for full Run 2 after preselection. The distributions are separately shown for electron... 113
Figure 5.12. Transverse mass of lepton and missing transverse energy distributions for full Run 2 after preselection. The distributions are separately shown... 114
Figure 5.13. Azimuthal angle difference of lepton and missing transverse energy distributions for full Run 2 after preselection. The distributions are separately... 115
Figure 5.14. mTeff distributions for full Run 2 after top pair process dominant control region selections in electron (left) and muon (right) channels with merged...[이미지참조] 127
Figure 5.15. mTeff distributions for full Run 2 after top pair process dominant control region selections in electron (left) and muon (right) channels with re-...[이미지참조] 127
Figure 5.16. mTeff distributions for full Run 2 after W process dominant control region selections in electron (left) and muon (right) channels with merged event topology.[이미지참조] 128
Figure 5.17. mTeff distributions for full Run 2 after W process dominant control region selections in electron (left) and muon (right) channels with resolved event topology.[이미지참조] 128
Figure 5.18. mTeff distributions for full Run 2 after Xbb (ℓ,ET) modeling control region selections in electron (left) and muon (right) channels with merged event topology.[이미지참조] 129
Figure 5.19. mTeff distributions for full Run 2 after Xqq (ℓ,ET) modeling control region selections in electron (left) and muon (right) channels with merged event topology.[이미지참조] 129
Figure 5.20. mTeff distributions for full Run 2 after Xbb (ℓ,ET) modeling control region selections in electron (left) and muon (right) channels with resolved event topology.[이미지참조] 130
Figure 5.21. mTeff distributions for full Run 2 after Xbq (ℓ,ET) modeling control region selections in electron (left) and muon (right) channels with resolved event topology.[이미지참조] 130
Figure 5.22. mTeff distributions for full Run 2 after Xqq (ℓ,ET) modeling control region selections in electron (left) and muon (right) channels with resolved event topology.[이미지참조] 131
Figure 5.23. mTeff distributions for full Run 2 after signal region merged Xbb selections in electron (left) and muon (right) channels.[이미지참조] 131
Figure 5.24. mTeff distributions for full Run 2 after signal region merged Xqq selections in electron (left) and muon (right) channels.[이미지참조] 132
Figure 5.25. mTeff distributions for full Run 2 after signal region resolved Xbb selections in electron (left) and muon (right) channels.[이미지참조] 132
Figure 5.26. mTeff distributions for full Run 2 after signal region resolved Xbq selections in electron (left) and muon (right) channels.[이미지참조] 133
Figure 5.27. mTeff distributions for full Run 2 after signal region resolved Xqq selections in electron (left) and muon (right) channels.[이미지참조] 133
Figure 5.28. Rate parameters for W and top pair processes derived from its dedicated control regions in different years. 136
Figure 5.29. Exclusion limits on mN - |VeN|2 parameter space.[이미지참조] 137
Figure 5.30. Exclusion limits on mN - |VµN|2 parameter space.[이미지참조] 138
Figure 5.31. Exclusion limits on mN - |VeN|2 (left) and mN - |VµN|2 (right) parameter space. SS dilepton and trilepton refers to the observed limit results...[이미지참조] 139
Figure 6.1. Three glasses. 142
Figure 6.2. Typical workflow of BSM search analysis at the LHC. The BSM events are stacked to the SM events and statistical analysis is performed, check-... 144
Figure 6.3. Inverting the workflow starting from already completed analysis from experiments. The new BSM events are stacked to the SM yields and sta-... 145
Figure 6.4. Schematic view of SMODELS workflow. 147
Figure 6.5. Exclusion limits set on mN - |VNℓ|2 plane. From the top to the bottom are exclusion limits for electron, muon, and tau only mixing scenarios,...[이미지참조] 155
Figure 6.6. The measurements of W boson mass from various experiments. The dark and light blue represents total and statistical uncertainties, respectively.... 157
Figure 6.7. Exclusion limits on M△±± - △M parameter space.[이미지참조] 164
Figure 6.8. Upper panel shows the representative differential cross section of highest mass dilepton pair distribution from four lepton measurement. Lower... 167