The Higgs Boson Produced With Top Quarks in Fully Hadronic Signatures (Springer Theses)

Description

The work presented in this PhD dissertation is the first search at CMS for Higgs bosons produced in association with top quarks (ttH) in a final state consisting of only jets. The results presented in this book uncover a new class of ttH events that will help us elucidate our understanding of the Yukawa sector interactions between the Higgs boson and the top quark. Despite this being the most common decay signature for ttH, a large contamination of SM backgrounds makes it the most challenging for extracting a signal from data. The PhD thesis presents many sophisticated tools and techniques that were developed in order to overcome these challenges. These tools pave the way for future analyses to investigate other standard model and beyond-standard model physics. Supervisor’s Foreword Abstract Acknowledgements Contents 1 Introduction References 2 Theoretical Background 2.1 The Standard Model of Particle Physics 2.1.1 The SM Lagrangian 2.2 The Higgs Sector 2.2.1 The Brout–Englert–Higgs Mechanism 2.2.2 Electroweak Interactions 2.2.3 The Standard Model Higgs Boson 2.3 Higgs Boson Properties 2.3.1 Theoretical Considerations 2.3.2 Higgs Boson Decays 2.3.3 Higgs Boson Production 2.4 Higgs Boson Measurements at the LHC 2.4.1 Decays to Vector Bosons 2.4.2 Decays to Fermions 2.4.3 Associated Production with Top Quarks 2.5 Fully Hadronic tbartH (Htobbarb ) Channel 2.5.1 Theoretical Cross Section 2.5.2 Standard Model Backgrounds References 3 Experimental Setup 3.1 The Large Hadron Collider 3.2 The CMS Detector 3.2.1 Silicon Pixel and Strip Trackers 3.2.2 Electromagnetic Calorimeter 3.2.3 Hadron Calorimeter 3.2.4 Muon Detectors 3.3 The CMS Trigger System 3.3.1 Level 1 Trigger 3.3.2 High Level Trigger 3.3.3 Trigger Maintenance 3.4 The CMS Data Acquisition System 3.4.1 DAQ Infrastructure 3.4.2 Flow Control and Operation References 4 Trigger and Object Reconstruction 4.1 Level 1 Trigger Selection 4.2 High Level Trigger Selection 4.2.1 Calorimeter Based Trigger 4.2.2 Particle Flow Based Trigger 4.3 Object Reconstruction 4.3.1 Particle Flow Algorithm 4.3.2 Primary Vertex 4.3.3 Muons 4.3.4 Electrons 4.3.5 Jets 4.3.6 B-Tagging 4.3.7 Quark-Gluon Discrimination References 5 The Matrix Element Method 5.1 Construction of the Phase Space 5.1.1 Reduction of the Dimensionality 5.1.2 Kinematic Reconstruction 5.2 Production and Decay Amplitude 5.2.1 Scattering Amplitude 5.2.2 Top Decay Amplitude 5.2.3 Higgs Decay Amplitude 5.3 Transfer Functions 5.3.1 Definition 5.3.2 Determination of Parameters 5.3.3 Checks and Validation 5.4 Event Probabilities 5.4.1 Permutations and Hypotheses 5.4.2 Numerical Integration 5.4.3 Validation and Performance 5.5 Likelihood Discriminant 5.5.1 Validation and Performance References 6 Analysis Strategy 6.1 Data and Simulation Samples 6.1.1 Data 6.1.2 Simulation Samples 6.2 Event Reweighting 6.2.1 Pileup Reweighting 6.2.2 Top pT Reweighting 6.2.3 Trigger Scale Factors 6.2.4 B-Tagging Scale Factors 6.2.5 Quark-Gluon Likelihood Reweighting 6.3 Event Selection 6.3.1 Preselection 6.3.2 Final Selection 6.4 Background Estimation 6.4.1 tbart+jets Background 6.4.2 QCD Multijet Background 6.5 Signal Extraction 6.6 Systematic Uncertainties References 7 Results and Combination 7.1 Statistical Tools 7.1.1 The Likelihood 7.1.2 Treatment of Systematic Uncertainties 7.1.3 Limit Setting 7.1.4 Significance of an Excess 7.2 Analysis Results 7.2.1 Maximum Likelihood Fit 7.2.2 Post-fit Distributions 7.2.3 Measurement of the Signal Strength 7.2.4 Comparison to Previous Results 7.3 Combination with Other Analyses References 8 Conclusions Appendix A MEM Studies A.1 QCD Matrix Elements A.2 Lost Quark Hypotheses A.3 B-Tagging Algorithms Appendix B Example Statistical Calculation B.1 Maximum Likelihood B.2 Upper Limits B.3 Significance Appendix References