Electroweak Gauginos with Highly Boosted Hadronically Decaying Bosons at the LHC (Springer Theses)

✍ Scribed by Yuta Okazaki

• Publisher: Springer
• Tongue: English
• Leaves: 230
• Category: Library

✦ Synopsis

Supersymmetry (SUSY) introduces superpartners of the Standard Model (SM) particles. If their masses are typically O(100 GeV) ∼ O(TeV), a lightest neutralino can be a candidate for the dark matter, and the problem is solved by canceling the correction of the Higgs boson mass. Further, SUSY can explain the experimental result of the muon magnetic moment (g-2).

This book presents a search for electroweakinos―the superpartners of the SM electroweak bosons―such as charginos and neutralinos using data at the LHC collected by the ATLAS detector. Pair-produced electroweakinos decay into the light ones and SM bosons (W/Z/h), and with the large mass difference between the heavy and light electroweakinos, the SM bosons have high momenta. In a fully hadronic final state, quarks decayed from the bosons are collimated, and can consequently be reconstructed as a single large-radius jet.

This search has three advantages. The first is a statistical benefit by large branching ratios of the SM bosons. The second is to use characteristic signatures―the mass and substructure―of jets to identify as the SM bosons. The last is a small dependency on the signal model by targeting all the SM bosons. Thanks to them, the sensitivity is significantly improved compared to the previous analyses.

Exclusion limits at the 95% confidence level on the heavy electroweakino mass parameter are set as a function of the light electroweakino mass parameter. They are set on wino or higgsino production models with various assumptions, such as the branching ratio of their decaying and the type of lightest SUSY particle. These limits are the most stringent limits. Besides, this book provides the most stringent constraints on SUSY scenarios motivated by the dark matter, the muon g-2 anomaly, and the naturalness.

✦ Table of Contents

Supervisor’s Foreword
Preface
Parts of this book have been published in the following journal articles
Acknowledgements
Contents
Acronyms
1 Introduction
References
2 Theoretical Background
2.1 The Standard Model
2.2 Supersymmetry
2.2.1 R-parity
2.2.2 SUSY Breaking
2.3 Minimal Supersymmetric Standard Model
2.3.1 Particle Contents in MSSM
2.3.2 Soft Breaking and the Soft Term in the MSSM Lagrangian
2.3.3 Gaugino Mass
2.3.4 SUSY Solutions of the SM Problems in the MSSM
2.3.5 Target Scenarios and Signal Models
2.3.6 Signal Topology
2.3.7 Current Limits by Collider Experiments
2.3.8 Current Limits by Other Experiments
2.4 Other SUSY Models
2.4.1 Soft Breaking Mechanism
2.4.2 General Gauge Mediation Scenario
2.4.3 Naturalness Driven Axino LSP Scenario
References
3 Experimental Apparatus
3.1 Large Hadron Collider
3.2 ATLAS Detector
3.2.1 Coordinate Systems in ATLAS
3.2.2 Magnet System
3.2.3 Inner Detector
3.2.4 Calorimeters
3.2.5 Muon Spectrometer
3.2.6 Trigger and Data Acquisition
References
4 Data and Monte Carlo Simulations
4.1 Recorded Data by the ATLAS Detector
4.2 Monte Carlo Simulation
4.2.1 Hard-Scatter Event Generation
4.2.2 SM Background Simulation
4.2.3 Signal Simulation Samples
References
5 Physics Object Reconstruction
5.1 Overview
5.2 Tracks, Vertices, and Topo-clusters
5.3 Jets
5.3.1 Large-R Jet
5.3.2 Small-R Jet
5.3.3 Track Jet
5.4 Electrons and Photons
5.5 Muons
5.6 Object Selection
5.7 Missing Transverse Energy
References
6 BosonTagging
6.1 Boosted W/Z Tagging
6.1.1 Overview
6.1.2 Optimization
6.1.3 Efficiency for Signal Jets
6.1.4 Efficiency for Background Jets
6.1.5 Physics Process Dependency
6.2 Vrightarrow bb Tagging Techinique
References
7 Event Selection
7.1 Selection Strategy
7.2 Trigger Selection and Event Cleaning
7.3 Discriminating Variables
7.4 Preselection
7.5 Signal Region Selection
7.5.1 SR-4Q
7.5.2 SR-2B2Q
References
8 Background Estimation
8.1 Strategy
8.2 Reducible Backgrounds Estimation
8.2.1 Overview
8.2.2 Control Regions
8.3 Validation for the Reducible Background Estimation
8.3.1 Preselection in 1L/1Y Categories
8.3.2 Definition of CRs and VRs in the 1L/1Y Categories
8.3.3 Comparison Between 0L/1L/1Y for V+jets MC
8.3.4 Jet Variable Comparison in the CRs and SRs/VRs
8.3.5 Transfer Factor Comparison
8.4 Physics Process Dependency in the Reducible Background Estimation and the Impact of the Composition Uncertainty
8.5 Irreducible Backgrounds Estimation
Appendix
References
9 Systematic Uncertainties
9.1 Large-R Jets
9.2 Boson Tagging Efficiency Uncertainty
9.3 Other Experimental Uncertainties
9.4 Theoretical Uncertainty
9.5 Summary of Systematic Uncertainties
References
10 Results
10.1 Background Determination
10.2 Results on the Signal Regions
10.3 Model-Specific Exclusion Limits
10.3.1 (tildeW,tildeB)-SIM
10.3.2 (tildeW,tildeB), (tildeH,tildeB), (tildeW,tildeH) and (tildeH,tildeW) Models
10.3.3 (tildeH,tildeG) Model
10.3.4 (tildeH,tildea) Model
References
11 Discussions
11.1 Future Prospects
11.1.1 Future Prospects of the Multi-lepton and Multi-b-and-1-Lepton analyses
11.1.2 Future Prospects of the Full-Hadronic Analysis
11.2 Implication to Dark Matter
11.2.1 tildeB-Like Dark Matter
11.2.2 tildeW-/tildeH-Like Dark Matter
11.3 Implication to Muon g-2 Anomaly
11.3.1 Light Electroweakino Scenarios Motivated by Muon g-2 Anomaly
11.4 Implication to Naturalness
References
12 Conclusions
Appendix A Supersymmetry Framework
A.1 Operator
A.2 Gaugino Mass Eigenstates
A.3 Grand Unified Theory
A.4 Couplings between Z/h and the Lightest Neutralino
A.5 Muon g-2 Contribution of SUSY Particles
A.6 Gauge Mediated Symmetry Breaking
Appendix B Event Cleaning
B.1 Event Cleaning Based on Detector Responses
B.2 Dead Tile Module Jets Veto
B.3 Non-collision Background Veto
B.4 Track Jets Cleaning
Appendix C Event Display