Heavy Neutral Particle Decays to Tau Pairs: Detected with CMS in Proton Collisions at \sqrt{s} = 7TeV (Springer Theses)

The work presented in this thesis spans a wide range of experimental particle physics subjects, starting from level-1 trigger electronics to the final results of the search for Higgs boson decay and℗ to tau lepton pairs. The thesis describes an innovative reconstruction algorithm for tau decays and details how it was instrumental in providing a measurement of Z decay to tau lepton pairs. The reliability of the analysis is fully established by this measurement before the Higgs boson decay to tau lepton pairs is considered. The work described here continues to serve as a model for analysing CMS Higgs to tau leptons measurements.℗ ℗ ℗ . Supervisor’s Foreword 7 Abstract 8 Acknowledgments 9 Contents 11 1 The Standard Model of Particle Physics 15 1.1 Historical Approach 15 1.2 Quarks, Leptons and Gauge Bosons 18 1.3 The Higgs Mechanism 20 1.4 Z and Higgs Boson Production in Proton Collisions 24 1.4.1 Z Boson Production in Proton Collisions 25 1.4.2 Higgs Boson Production in Proton Collisions 26 1.5 The Tau Lepton 28 References 28 2 Supersymmetry and the MSSM 30 2.1 The Minimal Supersymmetric Standard Model 32 2.2 The Higgs Sector in the MSSM 32 2.3 MSSM Higgs Production in Proton Collisions 34 References 35 3 Experimental Setup 36 3.1 The Large Hadron Collider 36 3.1.1 Performance Goals and Constraints 36 3.1.2 Layout and Operation 39 3.1.3 Operating Conditions in 2011 Run 41 3.2 The Compact Muon Solenoid Experiment 42 3.2.1 Coordinate System 42 3.2.2 Magnet 43 3.2.3 Inner Tracking System 44 3.2.4 Electromagnetic Calorimeter 47 3.2.5 Hadron Calorimeter 49 3.2.6 Muon System 50 3.2.7 Trigger 54 References 58 4 Event Simulation 59 4.1 Physics Event Generation 59 4.1.1 Hard Scattering Process 59 4.1.2 Parton Shower, Underlying Event and Hadronization 60 4.1.3 MC Generator Programs 61 4.1.4 K-factors 63 4.2 Detector Simulation 63 4.2.1 Simulation of Multiple Interactions 64 4.3 Simulated Samples 64 References 66 5 Event Reconstruction 67 5.1 Track and Vertex Reconstruction 67 5.1.1 Track Reconstruction 67 5.1.2 Iterative Tracking 68 5.1.3 Vertex Reconstruction 68 5.2 Electron Reconstruction and Identification 69 5.2.1 ECAL Seeded Reconstruction 69 5.2.2 Track Seeded Reconstruction 70 5.2.3 Rejection of Electrons from Converted Photons 71 5.2.4 Electron Identification 71 5.2.5 Electron Trigger 72 5.3 Muon Reconstruction and Identification 72 5.3.1 Standalone Muon Reconstruction 72 5.3.2 Global Muon Reconstruction 73 5.3.3 Tracker Muon Reconstruction 73 5.3.4 Muon Identification 74 5.3.5 Muon Trigger 74 5.4 Particle Flow Reconstruction 75 5.4.1 Calorimeter Clustering 76 5.4.2 Link Algorithm 76 5.4.3 Particle Reconstruction 77 5.5 Lepton Isolation 78 5.5.1 Isolation Optimization at Higher Luminosities 80 5.6 Jet and Missing Transverse Energy Reconstruction 82 5.6.1 Jet Reconstruction 82 5.6.2 Jet Energy Corrections 83 5.6.3 Missing ET Reconstruction 85 5.7 Identification of Jets Originating by b Quarks 85 5.7.1 The Track Counting Algorithm 86 References 87 6 Hadronic Tau Identification and Trigger 88 6.1 Decay Mode Based Reconstruction 88 6.2 The HPS Tau Identification Algorithm 89 6.2.1 Reconstruction of π0 Sub-Clusters 90 6.2.2 Combination of Charged Hadrons and Strips 90 6.2.3 Hadronic Tau Isolation 92 6.3 Discrimination Against Electrons and Muons 93 6.3.1 Muon Rejection 93 6.3.2 Electron Rejection 94 6.4 Performance of Tau Identification 94 6.4.1 Tau Performance in Simulation 95 6.4.2 Measurement of the Tau Fake Rate 96 6.5 Trigger for di-tau Final States 98 6.5.1 High Level Trigger Algorithm 98 6.5.2 Performance 100 References 100 7 Selection of Tau Pairs 101 7.1 Data Samples and Triggers 101 7.2 Object Selection 103 7.3 Topological Requirements 103 7.4 Corrections to the Simulation 107 7.4.1 Pileup Corrections 108 7.4.2 Electron and Muon Efficiency Corrections 108 7.4.3 Tau Efficiency Corrections 110 7.4.4 Missing ET Calibration 112 7.4.5 Corrections to the Topological Requirements 114 7.5 Background Estimation in e + τh and μ+ τh Final States 115 7.5.1 QCD Multijet 115 7.5.2 W +Jets 117 7.5.3 z+Jets 117 7.5.4 Top Pairs, di-bosons and γ+Jets 118 7.5.5 Background Estimation Method 118 7.6 Background Estimation for the e + μ Final State 120 7.7 Results 122 References 122 8 Measurement of Production 123 8.1 Acceptance Model 123 8.2 Systematic Uncertainties 124 8.2.1 Experimental Systematics 124 8.2.2 Theoretical Uncertainties 125 8.3 Combined Fit 125 8.4 Results 128 References 130 9 Search for Higgs Bosons 131 9.1 Event Selection and Categorization 131 9.2 Background Estimation 136 9.2.1 QCD and W Background Estimation 136 9.3 Normalization of Background for Higgs Searches 141 9.4 Systematic Uncertainties 142 9.5 Combined Fit 143 9.5.1 Definition of the SM Signal Model 144 9.5.2 Definition of the MSSM Signal Model 144 9.5.3 Statistical Analysis 145 9.6 SM Higgs Results 147 9.7 MSSM Higgs Results 148 References 149 10 Synopsis 150 AppendixCalorimeter Trigger Upgrade For HigherLuminosities 152 Front Matter....Pages i-xvi The Standard Model of Particle Physics....Pages 1-15 Supersymmetry and the MSSM....Pages 17-22 Experimental Setup....Pages 23-45 Event Simulation....Pages 47-54 Event Reconstruction....Pages 55-75 Hadronic Tau Identification and Trigger....Pages 77-89 Selection of Tau Pairs....Pages 91-112 Measurement of $$Z\rightarrow \tau \tau $$ Z → τ τ Production....Pages 113-120 Search for Higgs Bosons....Pages 121-139 Synopsis....Pages 141-142 Back Matter....Pages 143-152