Search for dark matter with ATLAS : using events with a highly energetic jet and missing transverse momentum in proton-proton collisions at √[racine carrée]s = 8 TeV : doctoral thesis accepted by the Johannes Gutenberg University, Mainz, Germany

La 4e de couverture indique : « This thesis describes in detail a search for weakly interacting massive particles as possible dark matter candidates, making use of so-called mono-jet events. It includes a detailed description of the run-1 system, important operational challenges, and the upgrade for run-2. The nature of dark matter, which accounts for roughly 25% of the energy-matter content of the universe, is one of the biggest open questions in fundamental science. The analysis is based on the full set of proton-proton collisions collected by the ATLAS experiment at the Large Hadron Collider at √s = 8 TeV. Special attention is given to the experimental challenges and analysis techniques, as well as the overall scientific context beyond particle physics. The results complement those of non-collider experiments and yield some of the strongest exclusion bounds on parameters of dark matter models by the end of the Large Hadron Collider run-1. Details of the upgrade of the ATLAS Central Trigger for run-2 are also included. » Supervisor’s Foreword 7 Abstract 9 Contents 11 1 Introduction 16 References 19 Part I Theory and Motivation 20 2 The Standard Model of Particle Physics 21 2.1 Survey of Fundamental Particles and Their Interactions 21 2.2 Electroweak Interaction and Symmetry Breaking 24 2.3 Quantum Chromodynamics 29 2.4 Open Questions and Extensions 31 References 33 3 Dark Matter 35 3.1 Basics of Cosmology 35 3.2 Relic Density 38 3.3 Evidence for Dark Matter 40 3.4 Dark Matter Candidates 45 3.5 WIMP Searches 48 3.5.1 Direct Detection 48 3.5.2 Indirect Detection 53 References 54 4 Proton-Proton Collisions 58 4.1 Terminology 58 4.2 Parton Density Functions 59 4.3 Cross Sections 62 4.4 Event Simulation 67 4.4.1 Final State Particle Generation 68 4.4.2 Event Generators 70 References 71 5 Mono-Jet Events as Dark Matter Signature at Colliders 74 5.1 Mono-Jet Signature of WIMP Pair Production 74 5.2 Effective Field Theory for Maverick Dark Matter 75 5.2.1 Validity of the Effective Theory 78 5.3 Simplified Models 80 5.4 Standard Model Background Processes 81 5.5 Mono-X Results After 2011 82 References 84 Part II Experimental Facilities 86 6 The Large Hadron Collider 87 6.1 The Accelerator Complex 87 6.2 The LHC Bunch Structure 88 6.3 Luminosity 89 6.4 The LHC Experiments 90 6.5 Performance and Perspectives 91 References 93 7 The ATLAS Experiment 94 7.1 General Information 94 7.1.1 The Coordinate System 94 7.1.2 Variables Used to Describe Particle Properties 95 7.1.3 Detector Overview 95 7.2 Tracking System 97 7.2.1 The Pixel Detector 98 7.2.2 The Semi-Conductor Tracker 98 7.2.3 The Transition Radiation Tracker 99 7.3 Calorimeter System 99 7.3.1 Electromagnetic Calorimeter 100 7.3.2 Hadronic Calorimeter 102 7.4 Muon System 103 7.5 Special Systems 104 7.5.1 Forward Detectors 105 7.5.2 Beam Pickup Systems 105 7.5.3 Beam Conditions Monitors 105 7.6 Trigger System 106 7.6.1 Overview 106 7.6.2 Level-1 Trigger 107 7.6.3 Central Trigger 110 7.7 Data Handling 113 7.7.1 Data Taking 113 7.7.2 Data Processing and Storage 114 7.8 Detector Simulation 115 7.9 Object Reconstruction 116 7.9.1 Electrons 116 7.9.2 Muons 117 7.9.3 Jets 118 7.9.4 Missing Transverse Energy 120 7.10 Luminosity Determination 122 References 124 Part III Operation and Upgrade of the Central Trigger 126 8 Operation of the Central Trigger During Run-I 127 8.1 Orbit Monitoring 128 8.2 Bunch Group Monitoring 129 8.2.1 Histogram Digitisation 130 8.2.2 Comparing Bunch Patterns 132 8.2.3 Application to Real Data 135 8.3 Testing of Trigger Menus 139 References 140 9 Upgrade of the Central Trigger 141 9.1 Upgrade of the Hardware During the Long-Shutdown-I 142 9.2 Central Trigger Simulation 144 9.2.1 Event Format 145 9.2.2 Inputs and Internal Objects 147 9.2.3 Simulation of Special Triggers 147 9.2.4 Trigger Decision 148 9.2.5 Output 148 9.2.6 Modifications for Running on Data 149 9.2.7 Data Quality Monitoring 149 9.3 Upgrade of the Central Trigger Simulation 151 9.3.1 Updated Event Format 151 9.3.2 New Software Packages 153 9.3.3 Adaption to New Hardware 155 References 156 Part IV Analysis 157 10 Analysis Strategy 158 10.1 Signal Characteristics and Parameters 158 10.2 Estimation of Main Background Contributions 159 10.2.1 Transfer from Control Regions 159 10.2.2 Method for Combination of Z(rightarrowνbarν)+jets Estimates 163 10.3 Small Background Contributions 164 10.4 Statistical Analysis 165 References 167 11 Data and Simulated Samples 168 11.1 Data 168 11.2 Simulated Samples 169 11.2.1 Signal Process 170 11.2.2 Background Processes 171 References 177 12 Physics Objects Definitions 179 12.1 Jets 179 12.2 Electrons 180 12.3 Muons 181 12.4 Missing Transverse Energy 182 References 183 13 Event Selection 184 13.1 Preselection 184 13.2 Optimisation Studies 186 13.2.1 Quantification of Sensitivity 186 13.2.2 Cut Studies 189 13.3 Complete Signal Region Selection 199 References 200 14 Background Estimation 201 14.1 Systematic Uncertainties 202 14.1.1 Trigger 202 14.1.2 Jet Energy Scale and Resolution 202 14.1.3 Lepton Uncertainties 203 14.1.4 Soft Terms in Missing Transverse Energy 204 14.1.5 Pile-Up 205 14.1.6 Track Veto 205 14.1.7 Luminosity 205 14.1.8 Background Subtraction in the Control Regions 205 14.1.9 PDF 206 14.1.10 Shower Modeling 207 14.1.11 Matching Scale 207 14.1.12 Renormalisation and Factorisation Scales 207 14.1.13 Electroweak Radiative Corrections on the W to Z Ratio 208 14.2 Estimation of Z(rightarrowνbarν)+jets Background 208 14.2.1 Estimation from a Z+jets Control Region with Two Muons 208 14.2.2 Estimation from a Z+jets Control Region with Two Electrons 220 14.2.3 Estimation from a W+jets Control Region with a Muon 226 14.2.4 Estimation from a W+jets Control Region with an Electron 235 14.2.5 Combination of Z(rightarrowνbarν)+jets Estimates 242 14.3 Estimation of Wpm(rightarrowellpmν)+jets Backgrounds 244 14.3.1 Wpm(rightarrowμpmν)+jets Estimation from a W+jets Control Region with a Muon 244 14.3.2 Wpm(rightarrowepmν)+jets and Wpm(rightarrowτpmν)+jets Estimation from a W+jets Control Region with an Electron 245 14.4 Z(rightarrowell+ell-)+jets Backgrounds Taken from Simulation 252 14.5 Top and Diboson Backgrounds 253 14.6 Multi-jet and Non-collision Background 254 References 255 15 Results and Interpretation 257 15.1 Background Summary and Model Independent Results 257 15.2 Inputs for Limit Calculation 262 15.2.1 Luminosity 263 15.2.2 Jet Energy Scale and Resolution 263 15.2.3 ETmiss Soft Terms 264 15.2.4 Beam Energy 264 15.2.5 Factorisation and Renormalisation Scale 265 15.2.6 PDF 265 15.2.7 ISR and FSR 266 15.3 Dark Matter Limits 267 15.3.1 Effective Operator Limits 267 15.3.2 Simplified Model 277 15.4 Results Summary 280 References 280 16 Prospects with Future LHC Data 283 16.1 Estimation of Event Yields 283 16.2 Reach of the Mono-Jet Search in the EFT Framework 285 16.3 Comparison to a Simplified Model 289 16.4 Summary of 14TeV Studies 290 References 291 Part V Conclusion 292 17 Conclusion 293 Appendix ASignal Simulation Samples 297 Appendix BSignal Tables 303 Curriculum Vitae 324 Front Matter....Pages i-xv Introduction....Pages 1-4 Front Matter....Pages 5-5 The Standard Model of Particle Physics....Pages 7-20 Dark Matter....Pages 21-43 Proton-Proton Collisions....Pages 45-60 Mono-Jet Events as Dark Matter Signature at Colliders....Pages 61-72 Front Matter....Pages 73-73 The Large Hadron Collider....Pages 75-81 The ATLAS Experiment....Pages 83-114 Front Matter....Pages 115-115 Operation of the Central Trigger During Run-I....Pages 117-130 Upgrade of the Central Trigger....Pages 131-146 Front Matter....Pages 147-147 Analysis Strategy....Pages 149-158 Data and Simulated Samples....Pages 159-169 Physics Objects Definitions....Pages 171-175 Event Selection....Pages 177-193 Background Estimation....Pages 195-250 Results and Interpretation....Pages 251-276 Prospects with Future LHC Data....Pages 277-285 Front Matter....Pages 287-287 Conclusion....Pages 289-292 Back Matter....Pages 293-322