Search for Muon Neutrino to Electron Neutrino Oscillations in the MINOS Experiment (eBook)

Supervisor’s Foreword 6
Acknowledgments 8
Contents 10
1 Introduction 14
2 Neutrino Physics 17
2.1…A Historical Look at the Neutrino 17
2.1.1 Proposal and Discovery 17
2.1.2 Neutrinos in the Standard Model 20
2.1.2.1 Basic Ingredients of the Standard Model 20
2.1.2.2 Weak Interactions in the Standard Model 22
Theoretical formalism 22
2.1.2.3 Neutrino Mass in the Standard Model 27
2.1.3 Beyond the Standard Model 28
2.1.3.1 Vindication of the Standard Model 28
2.1.3.2 The Discovery of Neutrino Oscillations 29
2.2…Neutrino Oscillations 32
2.2.1 Theoretical Formalism 32
2.2.1.1 General Case 32
2.2.1.2 Three-Flavor Neutrino Mixing 33
2.2.1.3 Two-Flavor Approximation 34
2.2.1.4 Matter Effects 36
2.2.2 Precision Measurements of Neutrino Oscillations 38
2.3…Open Questions in Neutrino Physics 40
2.3.1 General Questions 40
2.3.2 Questions Addressed by This Thesis 43
References 46
3 The MINOS Experiment 50
3.1…An Overview of the Experiment 50
3.2…The NuMI Neutrino Beam 51
3.2.1 Basic Principle 51
3.2.2 Description of the Main Components 52
3.2.3 Beam Configuration 54
3.2.4 Composition 55
3.3…The MINOS Detectors 55
3.3.1 Detector Technology 55
3.3.1.1 Basic Principle 56
3.3.1.2 Light Collection 57
3.3.1.3 Magnetic Field 58
3.3.2 The Far Detector 58
3.3.3 The Near Detector 61
3.4…MINOS Data 63
3.4.1 MINOS Beam Data 63
3.4.2 MINOS Monte-Carlo Simulation 65
3.4.2.1 Simulation of the Beam 65
3.4.2.2 Simulation of the Neutrino Interactions 66
3.4.2.3 Simulation of the Detectors 67
3.4.3 MINOS Reconstruction 68
3.5…Calibration 70
3.5.1 Relative Calibration 70
3.5.1.1 Energy Branch 70
Drift correction 70
Linearity correction 71
Strip-to-strip correction 71
Transverse position correction 72
Inter-detector energy scale 72
3.5.1.2 Photoelectron Branch 73
3.5.2 Absolute Calibration 74
3.5.3 Implementation in the Simulation 75
References 76
4 Measuring /boldtheta_{/bf{13}} in MINOS 78
4.1…The Search for /boldnu_{/rm/bf e} Appearance in MINOS 78
4.1.1 Brief Motivation Review 78
4.1.2 A Direct Handle on /boldtheta_{/bf{13}} 79
4.1.3 Backgrounds to the Search 82
4.1.3.1 Identifying the Neutrino Flavor 82
4.1.3.2 Hadronic vs. EM Showers 84
4.1.3.3 Summary of Backgrounds 88
4.2…The Overall Strategy for the Analysis 88
4.2.1 The Keys to Maximizing the Reach 88
4.2.2 Identifying /boldnu_{/bf{e}} CC Events 90
4.2.3 Predicting the Backgrounds 91
4.2.3.1 General Strategy 91
4.2.3.2 Near Detector Decomposition 92
4.2.3.3 Extrapolating the Backgrounds to the Far Detector 93
4.2.4 A Blind Analysis 93
References 94
5 A Novel Approach for Selecting /boldnu_{/bi e} CC Events 95
5.1…The Philosophy of Our Approach 95
5.2…A Preselection for /boldnu_{/bi e} CC Events 96
5.2.1 Selecting Events in the Fiducial Volume 96
5.2.2 Removing the Obvious Background 96
5.2.3 Performance 99
5.3…The Workings of the LEM Algorithm 100
5.3.1 Basic Principle 100
5.3.2 The Library 102
5.3.3 Compacting Events 102
5.3.3.1 Light Attenuation 102
5.3.3.2 The Compacting Procedure 104
5.3.4 Event Comparison 105
5.3.4.1 The Comparison Metric 105
5.3.4.2 Implementation in the Algorithm 107
5.3.4.3 Selecting the Events Worth Matching 109
5.4…Making the Most of the LEM Selection 110
5.4.1 The Information from the Best Matches 110
5.4.2 Optimizing the Selection Basics 111
5.4.2.1 A Simple LEM Selection 111
5.4.2.2 Number of Best Matches 111
5.4.2.3 Library Composition 112
5.4.3 The LEM PID 113
5.4.3.1 Obtaining a Quick Data-Based Far Detector Prediction 117
5.4.3.2 Cut Value Optimization 121
5.5…Characteristics of LEM 122
5.5.1 Selected Events 122
5.5.2 Preliminary Relative Sensitivity to /boldtheta_{/bf 13} 124
References 125
6 Measuring the Backgrounds in the Near Detector 126
6.1…The Need for the Near Detector 126
6.1.1 Uncertainties in the Simulation 126
6.1.2 The Near Detector’s Role in the Analysis 130
6.2…The Intrinsic Beam /boldnu_{/bi e} Component 132
6.2.1 Origin 132
6.2.2 Beam /boldnu_{/bi e}’s in the Simulation 133
6.2.3 Cross-Check with Antineutrinos 134
6.3…The Horn-On/Horn-Off Decomposition Method 135
6.3.1 Basic Concept 135
6.3.2 Description of the Method 136
6.3.3 Uncertainties in the Decomposition 137
6.3.4 Results 141
6.4…The Muon-Removal Decomposition Method 141
6.4.1 Basic Principle 141
6.4.2 Obtaining a Sample of Muon-Removed Events 142
6.4.2.1 The Muon-Removal Algorithm 142
6.4.2.2 Ensuring the Quality of Muon-Removed Events 142
6.4.2.3 Data-MC Discrepancy with Muon-Removed Events 144
6.4.3 Decomposing the Near Detector Spectrum 145
6.4.3.1 Description of the Method 145
6.4.3.2 Systematic Uncertainties 148
6.4.3.3 Results 150
6.5…Comparison of Near Detector Decomposition Results 150
References 151
7 Predicting the Far Detector Rates 152
7.1…Far Detector Background Rates 152
7.1.1 Flux Differences between the Two Detectors 152
7.1.2 Choice of Extrapolation Method 154
7.1.2.1 The Mechanics of the Extrapolation 156
7.1.2.2 Oscillated {{/varvec /nu}_{{/varvec /tau}}} CC and {{/varvec /nu}_{{/varvec e}}} CC Events 158
7.1.2.3 Predicted Background Rates 160
7.2…Expected Far Detector Signal Rate 162
7.2.1 Overview 162
7.2.2 Electrons in CalDet 162
7.2.3 The Impact of Hadronic Shower Mismodeling 164
7.2.3.1 Uncertainties in the Hadronic Model 164
7.2.3.2 A Data-Based Correction from MRE Events 164
7.3…Summary of the Far Detector Predictions 168
References 170
8 Systematic Errors and theta 13 Sensitivity 171
8.1…Systematic Uncertainties 171
8.1.1 Overview 171
8.1.2 Uncertainties in the Physics Models 172
8.1.2.1 Uncertainties in the Hadronic Model 172
8.1.2.2 Uncertainties in the Cross-Sections 174
8.1.2.3 Uncertainties in the Beam Flux 175
8.1.2.4 Uncertainties in the Intranuclear Rescattering Model 176
8.1.3 Uncertainties in the Detector Models 176
8.1.3.1 Uncertainties in the Low Pulse Height Hits 176
8.1.3.2 Uncertainties in the Crosstalk Model 177
8.1.3.3 Uncertainties in the Calibration 181
8.1.3.4 Uncertainties in the Energy Scale 182
8.1.3.5 Uncertainties in Neutrino Intensity 183
8.1.3.6 Uncertainties in the Preselection 184
8.1.3.7 Uncertainties in the Normalization 184
8.1.3.8 Additional Uncertainties for Oscillated {/varvec /nu}_{{/varvec /tau}}/,/hbox{CC} and {/varvec /nu}_{/bf e}/,/hbox{CC} Events 184
8.1.4 Summary of Systematic Uncertainties 185
8.1.4.1 Simulation Uncertainties 185
8.1.4.2 Combining all the Uncertainties on the Prediction 185
8.1.4.3 Contributions from the Extrapolation 188
8.1.4.4 Contributions from the Decomposition 194
8.1.4.5 Total Systematic Uncertainty on the Background 195
8.2…Overall Physics Reach 195
8.2.1 Number of Selected Events 195
8.2.2 Expected Sensitivity Contours 197
8.2.2.1 A Feldman--Cousins Approach 197
8.2.2.2 Expected Exclusion Limits 198
8.2.2.3 Discovery Potential 200
References 201
9 Far Detector Data Analysis and nu e Appearance Results 203
9.1…Far Detector Sidebands 203
9.1.1 The Anti-LEM Sideband 203
9.1.2 The MRE Sideband 207
9.1.3 The MRCC Sideband 208
9.2…Addressing the MRCC Sideband Excess 211
9.2.1 Systematics in the MRCC Sample 211
9.2.2 Comparison with Perfect Muon-Removed Events 214
9.2.3 The Energy of the MRCC Parents 216
9.2.4 Making a Decision 218
9.3…Electron Neutrino Appearance Results 220
9.3.1 Number of Selected Events 220
9.3.1.1 General Results 220
9.3.1.2 Consistency Checks 220
9.3.1.3 Comparison with the MRCC Sideband 224
9.3.2 Resulting Limits on /boldtheta_{/bf 13} 225
References 228
10 Pushing the Neutrino Frontier 229
10.1…The Search for a Nonzero theta 13 229
10.1.1 The Next nu e Appearance Analysis 229
10.1.1.1 Reduction of Systematic Errors 229
10.1.1.2 Expected Limits 231
10.1.2 Beyond {/bf 7.0/times10^{20}} POT 232
10.2…Antineutrino Physics 234
10.2.1 Antineutrinos in MINOS 234
10.2.2 Grasping the Opportunity 236
10.2.2.1 MINOS’ Unique Advantage 236
10.2.2.2 Physics with Antineutrinos 238
Antineutrino Appearance 238
Antineutrino Disappearance 239
10.2.2.3 Initial Results 240
10.2.3 A Proposal for Antineutrino Running 242
10.2.3.1 Motivation 242
10.2.3.2 The Basics of Reversed Horn Current Running 243
10.2.3.3 Expected Sensitivities 244
10.2.3.4 The Time for Reversed Horn Current Running 246
10.3…Conclusions 247
References 247
Appendix A 
249 
A.1 Brief Overview of the Veto Shield 249
A.1.1 Motivation 249
A.1.2 Veto Shield Configuration 250
A.2 Implementation of New Software Tools 251
A.2.1 Veto Shield Geometry 251
A.2.2 Veto Shield Traceback 252
A.2.2.1 Technical Implementation 252
A.2.2.2 Traceback Resolution 253
A.3 Identification of Hardware Problems 254
A.4 Time Calibration of the Veto Shield 255
A.4.1 Mechanism of the Calibration 255
A.4.2 Performance of the Calibration 259
A.5. Impact on Atmospheric Neutrino Analyses 260
Appendix B 
262 
B.1 Attenuation Corrections 262
B.1.1 Basics 262
B.1.2 Far Detector Corrections 263
B.1.3 Near Detector Corrections 265
B.1.3.1. Differences and Strategy 265
B.1.3.2. Matching the Two Detectors 266
B.1.3.3 Matching Performance 267
B.1.4 Selection Efficiencies 268
B.2 Sorting Technical Constraints 272
B.2.1 Time 272
B.2.2 Memory 272
Appendix C A Measurement of Beam v_e's 
274 
C.1 Introduction 274
C.2 Underlying Principle 274
C.3 Description of the Method 276
C.4 Antineutrino Selection 278
C.5 Systematic Uncertainties 280
C.5.1 Beam Optics 281
C.5.2 Hadron Production 282
C.5.3 Background 282
C.5.4 Antineutrino Detection Efficiency 283
C.5.5 Antineutrino Cross-Section 283
C.5.6 Relative me and ml Cross-Sectional Uncertainty 284
C.6 Results and Conclusions 284
Appendix D Feldman–Cousins Framework for the ml ! me 
287 
D.1 General Implementation 287
D.1.1 Motivation 287
D.1.2 Procedure 287
D.1.3 Obtaining Smooth Contours 289
D.2 Incorporating the Uncertainties on the Oscillation 
291 
D.2.1 Motivation 291
D.2.2 Technical Challenges 292
D.2.3 First Solution 292
D.2.4 Second Solution 295
References 297
Index 299