Techniques for Inelastic Effective Field Theory Measurements with The
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Techniques for Inelastic Effective Field Theory Measurements with the Large Underground Xenon Experiment by Daniel Patrick Hogan A dissertation submitted in partial satisfaction of the requirements for the degree of Doctor of Philosophy in Physics in the Graduate Division of the University of California, Berkeley Committee in charge: Professor Robert Jacobsen, Chair Professor Marjorie Shapiro Professor Kai Vetter Summer 2018 Techniques for Inelastic Effective Field Theory Measurements with the Large Underground Xenon Experiment Copyright 2018 by Daniel Patrick Hogan 1 Abstract Techniques for Inelastic Effective Field Theory Measurements with the Large Underground Xenon Experiment by Daniel Patrick Hogan Doctor of Philosophy in Physics University of California, Berkeley Professor Robert Jacobsen, Chair Cosmological evidence indicates that nonbaryonic dark matter makes up a quarter of the energy density of the universe. One hypothesis for the particle nature of dark matter is the weakly-interacting massive particle (WIMP). The Large Underground Xenon (LUX) experiment is a dual-phase xenon WIMP search experiment with a 250kg active volume. Computational tools developed to support LUX analyses include data mirroring and a data visualization web portal. Within the LUX detector, particle interactions produce pulses of scintillation light. A pulse shape discrimination (PSD) technique is shown to help classify interaction events into nuclear recoils and electron recoils based on the time-structure of the pulses. This approach is evaluated in the context of setting limits on inelastic effective field theory (IEFT) dark matter models. Although PSD is not found to provide significant improvement in the limits, LUX is nevertheless able to set world-leading limits on some IEFT models, while limits for other IEFT models are reported here for the first time. i Felix qvi potvit rervm cognoscere cavsas {Virgil ii Contents Contents ii List of Figures v List of Tables viii Introduction x 1 Physics of Dark Matter 1 1.1 Cosmological Motivation for Dark Matter . 1 1.1.1 Early Clues . 1 1.1.2 Composition of the Universe . 3 1.1.3 Matter and Dark Energy . 5 1.1.4 Baryonic and Dark Matter . 8 1.2 Dark Matter Candidates . 11 1.2.1 WIMPs . 11 1.2.2 Axions . 16 1.2.3 Other Dark Matter Theories . 17 1.2.4 Detection Approaches . 19 1.3 WIMP Dark Matter Direct Detection . 20 1.3.1 WIMP/Nucleus Coupling: Spin-Independent and Spin-Dependent . 21 1.3.2 \Heavy Neutrino" Model . 22 1.3.3 Normalized Cross-sections, and the Need for New Models . 27 1.3.4 Supersymmetry . 28 1.3.5 Effective Field Theory . 31 1.3.6 Coherent Neutrino Scattering . 32 1.3.7 Experimental Limits . 33 1.4 WIMP Direct Detection Experiments . 38 1.4.1 Two-Channel Discrimination . 38 1.4.2 One-Channel Discrimination . 40 2 LUX Hardware and Operation 42 iii 2.1 Detector Overview . 42 2.2 Location . 43 2.3 Hardware Systems . 44 2.3.1 Shielding . 44 2.3.2 Target, Grids, and PTFE . 45 2.3.3 Circulation and Purification . 46 2.3.4 Photomultiplier Tubes . 47 2.4 Signal Processing . 49 2.4.1 Amplification and Digitization . 49 2.4.2 Data Processing . 49 2.4.3 Data Analysis . 50 2.5 Detector Calibration . 51 2.5.1 Kr-83m . 51 2.5.2 Tritium . 53 2.5.3 D-D Neutrons . 54 2.6 Run 3 and Run 4 . 55 3 Data Storage and Visualization 58 3.1 LBL NERSC Data Mirror . 58 3.1.1 Why a Mirror? . 58 3.1.2 Infrastructure . 59 3.1.3 Software Layout . 59 3.2 Visualux . 63 3.2.1 Communication . 65 3.2.2 Backend Code . 65 3.2.3 Frontend Code . 67 3.2.4 Dataset Preview . 71 3.2.5 Example Pulses and Events . 72 4 Pulse Shape Discrimination 82 4.1 Physics of S1 Pulse Shapes . 82 4.1.1 The Energy Deposition Process . 82 4.1.2 ERs and NR Timescales . 84 4.1.3 Previous Pulse Shape Studies . 84 4.2 Pulse Shape Discrimination in LUX . 85 4.2.1 Calibration Data . 85 4.2.2 Calibration Cuts . 86 4.2.3 Prompt Fraction . 90 4.2.4 Model Building . 92 4.2.5 Model Implications . 98 4.3 Other PSD Figures of Merit . 102 4.3.1 Individual Photon Fitting . 102 iv 4.3.2 Machine Learning . 104 5 Inelastic Effective Field Theory 108 5.1 EFT Physics . 108 5.2 IEFT Parameter Space . 111 5.2.1 Regions of Parameter Space . 111 5.2.2 Calculating IEFT Recoil Spectra . 112 5.2.3 Selection of IEFT Models . 113 5.3 Profile Likelihood Ratio . 114 5.3.1 PLR Statistic . 114 5.3.2 Modifications to PLR Code . 117 5.4 Results . 119 5.4.1 Spin-Independent Dark Matter . 119 5.4.2 Inelastic Dark Matter . 121 5.4.3 A Novel IEFT Example . 122 5.4.4 IEFT Dark Matter Limits . 123 6 Next Steps 129 6.1 PSD for Limit Setting . 129 6.2 Preliminary Work Towards Higher Energies . 130 6.3 Conclusion . 133 Bibliography 134 v List of Figures 1.1 Velocity curves for 21 galaxies. 4 1.2 Three techniques for measuring Ωm and ΩΛ..................... 5 1.3 Cosmic microwave background anisotropy power spectrum, as measured by Planck. 7 1.4 Baryon acoustic oscillation correlation function, based on data from the Sloan Digital Sky Survey. 8 1.5 Primordial nuclei abundances from nucleosynthesis, as a function of either baryon- to-photon ratio or baryon density. 10 1.6 X-ray image of the Bullet Cluster, with overlaid mass contours from gravitational lensing. 10 1.7 Comoving number density (na3) of a cold thermal relic during freeze-out, as a function of mχ=T (which is proportional to a). 13 1.8 Potential with a spontaneously broken U(1) symmetry. 17 1.9 Feynman diagram of axion-photon coupling. 17 1.10 Feynman diagrams of the various approaches to detecting dark matter. 19 1.11 Feynman diagram of \heavy neutrino" dark matter scattering. 23 1.12 Spin-independent supersymmetric WIMP mass and cross-section phase space. 30 1.13 Feynman diagram of coherent neutrino scattering. 32 1.14 Anticipated background for spin-independent WIMP direct detection experiments due to coherent neutrino scattering (black) [47]. 33 1.15 Major current, planned, and recent dark matter direct detection experimental collaborations, sorted by detection methods. 39 1.16 Spin-independent normalized cross-section limits and supposed detections versus WIMP mass for recent experiments. 41 2.1 How LUX detects events. 43 2.2 A typical event in LUX. 44 2.3 Position, in terms of drift time and radius squared, for all events in the 85day LUX Run 3. 46 2.4 Key components inside the LUX cryostat. 47 2.5 LUX data transfers. 51 2.6 Electron recoil (top) and nuclear recoil (bottom) bands. 53 2.7 Tritium energy spectrum. 54 vi 2.8 S1 and S2 signals from D-D neutrons, in units of detected photoelectrons. 55 2.9 Spin-independent WIMP cross-section limits from LUX, including the Run 3 reanalysis, Run 4, and the combined Run 3 + Run 4 result. 56 3.1 Schematic of hardware and software systems involved in transferring data to the NERSC mirror. ..