| Description |
1 online resource (201 p.) |
| Series |
Springer theses |
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Springer theses.
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| Contents |
Intro -- Supervisor's Foreword -- Abstract -- Preface -- References -- Acknowledgements -- Contents -- Part I Theoretical Motivation -- 1 The Standard Model -- 1.1 Quantum Field Theory and Gauge Theory -- 1.1.1 Cross Sections and Decay Widths -- 1.1.2 Symmetries and Representations -- 1.2 Quantum Electrodynamics -- 1.3 Quantum Chromodynamics -- 1.4 Electroweak Unification -- 1.4.1 The Weak Force -- 1.4.2 Glashow-Weinberg-Salam Theory -- 1.4.3 Symmetry Breaking and the Higgs Mechanism -- 1.5 The Higgs Boson -- 1.6 Summary -- 1.6.1 Shortcomings of the Standard Model -- References |
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2 Physics Beyond the Standard Model -- 2.1 Supersymmetry -- 2.2 Models of Uncolored Naturalness -- 2.2.1 Folded SUSY -- 2.2.2 Twin Higgs -- 2.2.3 Quirky Little Higgs -- 2.3 Neutral Naturalness Phenomenology -- 2.3.1 Exotic Higgs Decays -- 2.3.2 Glueball Decays -- 2.4 Long-Lived Particles -- 2.5 Bottom-up Considerations -- 2.5.1 The Hidden Sector -- 2.5.2 A Simplified Model -- 2.6 Existing Constraints on Br(Hrightarrowss) -- References -- Part II Experimental Apparatus -- 3 The Large Hadron Collider and the ATLAS Detector -- 3.1 The Large Hadron Collider -- 3.1.1 Machine Design |
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3.1.2 Performance and Operation -- 3.2 The ATLAS Detector -- 3.2.1 The Inner Detector -- 3.2.2 Calorimeter -- 3.2.3 The Muon Spectrometer -- 3.2.4 Trigger -- References -- 4 Event Reconstruction -- 4.1 Track and Vertex Reconstruction -- 4.1.1 Track Reconstruction -- 4.1.2 Primary Vertex Reconstruction -- 4.2 Physics Object Reconstruction -- 4.2.1 Jets -- 4.2.2 Muons -- 4.2.3 Electrons -- 4.2.4 Photons -- References -- 5 Reconstruction of Long-Lived Particle Decays -- 5.1 Large Radius Tracking -- 5.1.1 LRT Performance -- 5.2 Displaced Vertex Reconstruction -- 5.2.1 Description of the Algorithm |
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5.2.2 Performance -- References -- Part III Search for Exotic Higgs Decays -- 6 Data and Simulated Samples -- 6.1 Simulation -- 6.1.1 Monte-Carlo Event Generation -- 6.1.2 Simulation of Higgs Boson Decays to Long-Lived Particles -- 6.1.3 Simulation of Z+jets Events -- 6.2 Data -- 6.2.1 Trigger -- 6.2.2 The RPVLL Stream -- References -- 7 Search for Higgs Decays to Long-Lived Particles -- 7.1 Event Selection -- 7.1.1 Preselection -- 7.1.2 Displaced Vertex Selection -- 7.1.3 Event Categorization -- 7.1.4 Analysis Cutflow -- 7.2 Background Estimation -- 7.2.1 Closure Test -- 7.2.2 Validation |
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7.2.3 Signal Injection Test -- 7.3 Signal Systematic Uncertainties -- 7.3.1 Uncertainties on Standard Objects -- 7.3.2 Uncertainties on Non-standard Reconstruction -- 7.3.3 Theory and Signal Modeling -- 7.3.4 Other Sources of Systematic Error -- 7.3.5 Summary of Uncertainties -- References -- 8 Results -- 8.1 Unblinded Results -- 8.2 Statistics -- 8.2.1 The Likelihood Function -- 8.2.2 Hypothesis Tests -- 8.2.3 Confidence Intervals and the CLs Method -- 8.3 Exclusion Limits on B(Hrightarrowaarightarrowboverlinebboverlineb) -- 8.3.1 Lifetime Reweighting -- 8.3.2 Limits -- 8.3.3 Better than Zero? |
| Summary |
This work describes a search for exotic decays of the Higgs boson to two long-lived, neutral, spin-0 particles which subsequently decay to pairs of b quarks, giving the striking signature of displaced hadronic jets in the ATLAS inner detector. Several other ATLAS searches have probed this decay topology previously, excluding branching ratios of the Higgs boson to long-lived particles (LLPs) of more than 10% for proper lifetimes greater than 100mm. These searches relied on dedicated triggers designed to select events with LLPs decaying in the ATLAS calorimeter or muon spectrometer. The lack of an equivalent trigger for LLP decays in the ATLAS inner detector has been a limiting factor in probing LLP lifetimes less than 100mm. To circumvent the difficulty of triggering on LLP decays, the search presented in this thesis exploits the ZH associated production mode, relying on leptonic trigger signatures to select interesting events. This is the first search for Higgs boson decays into LLPs to exploit this analysis methodology and additionally makes use of several novel methods for both background rejection and background estimation. No excess over Standard Model predictions is observed, and upper limits are set on the branching ratio of the Higgs boson to LLPs . Depending on the mass of the LLP, branching ratios greater than 10% are excluded for lifetimes as small as 4mm and as large as 100mm, probing an important gap in the ATLAS exotic Higgs decay programme. In comparison to the previous searches for Higgs decays to LLPs, these are among the most stringent limits placed on this scenario, and for LLPs with masses below 40 GeV these results represent the strongest existing constraints on the branching ratio of the Higgs boson to LLPs in this lifetime regime |
| Analysis |
Physics |
|
Science |
| Notes |
"Doctoral thesis accepted by University of Massachusetts Amherst, Amherst, USA." |
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8.3.4 Summary of Results |
| Bibliography |
Includes bibliographical references |
| Notes |
Online resource; title from PDF title page (SpringerLink, viewed June 5, 2023) |
| Subject |
Higgs bosons -- Decay
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| Form |
Electronic book
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| ISBN |
9783031304668 |
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3031304667 |
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