Study of Excess Electronic Recoil Events in XENON1T

Description

This thesis summarizes the original analysis work performed by the author on data from XENON1T, a search for dark matter with a ton-size noble liquid detector operated at Gran Sasso Underground Laboratory in Italy. The nature of dark matter is one of the most open and pressing questions of modern physics, and the unique data acquired with this detector allows the exploration and investigation of several potential scenarios. The analysis of Dr. Shockley searches for a class of elusive elementary particles that interact with the electrons of ordinary atoms, instead of the nucleus. Results of the analysis present, with high confidence, an excess with respect to the expected background. Beyond more mundane explanations, this additional rate of electron-mediated interactions might be a first hint of physics beyond the standard model. This accessible thesis provides details on the detector, the data, and the theory, delivering to the reader an in-depth and coherent picture of the search for physics beyond the standard model. Supervisor's Foreword Acknowledgments Contents 1 Searching for New Physics with XENON1T 1.1 The XENON1T Detector 1.1.1 The S1 Signal 1.1.2 The S2 Signal 1.1.3 Position Reconstruction 1.1.4 Particle Discrimination: Electronic vs. Nuclear Recoils 1.1.5 Background Reduction 1.2 Physics Reach of XENON1T 1.2.1 Solar Axions 1.2.2 Neutrino Magnetic Moment 1.2.3 Bosonic Dark Matter 2 Event Reconstruction and Selection 2.1 Energy Reconstruction and Resolution 2.1.1 Energy Reconstruction 2.1.2 Energy Resolution 2.2 Detection Efficiency 2.2.1 Single Photoelectron Acceptance 2.2.2 Reconstruction Efficiency 2.2.3 Efficiency as Function of Charge 2.2.4 Efficiency as Function of Reconstructed Energy 2.3 Event Selection 3 Background + Signal Modeling and Statistical Methods 3.1 Background Model 3.2 Signal Modeling 3.3 Statistical Framework 4 Results 4.1 Background-Only Fit 4.2 Investigating the Excess 4.3 Potential Backgrounds 4.3.1 Xenon X-Rays 4.3.2 37Ar 4.3.3 Tritium 4.4 Searches for New Physics in XENON1T ER Data 4.5 Search for Solar Axions 4.5.1 Main Results 4.5.2 Interpretation Under Specific QCD Models 4.5.3 Including Tritium as a Background 4.6 Search for an Enhanced Neutrino Magnetic Moment 4.6.1 Main Result 4.6.2 Including Tritium as a Background 4.7 Bosonic Dark Matter Results 4.8 Science Run 2 4.9 Time Dependence 4.10 Updated Analysis 4.10.1 Summary of Updates 4.10.2 Results of Updated Analysis 5 Conclusions and Outlook 5.1 Summary 5.2 Outlook: XENONnT 5.3 Conclusion References