The Long-Baseline Neutrino Experiment: Exploring Fundamental Symmetries of the Universe

The preponderance of matter over antimatter in the early Universe, the dynamics of the supernova bursts that produced the heavy elements necessary for life and whether protons eventually decay --- these mysteries at the forefront of particle physics and astrophysics are key to understanding the early evolution of our Universe, its current state and its eventual fate. The Long-Baseline Neutrino Experiment (LBNE) represents an extensively developed plan for a world-class experiment dedicated to addressing these questions. LBNE is conceived around three central components: (1) a new, high-intensity neutrino source generated from a megawatt-class proton accelerator at Fermi National Accelerator Laboratory, (2) a near neutrino detector just downstream of the source, and (3) a massive liquid argon time-projection chamber deployed as a far detector deep underground at the Sanford Underground Research Facility. This facility, located at the site of the former Homestake Mine in Lead, South Dakota, is approximately 1,300 km from the neutrino source at Fermilab -- a distance (baseline) that delivers optimal sensitivity to neutrino charge-parity symmetry violation and mass ordering effects. This ambitious yet cost-effective design incorporates scalability and flexibility and can accommodate a variety of upgrades and contributions. With its exceptional combination of experimental configuration, technical capabilities, and potential for transformative discoveries, LBNE promises to be a vital facility for the field of particle physics worldwide, providing physicists from around the globe with opportunities to collaborate in a twenty to thirty year program of exciting science. In this document we provide a comprehensive overview of LBNE's scientific objectives, its place in the landscape of neutrino physics worldwide, the technologies it will incorporate and the capabilities it will possess.Comment: Major update of previous version. This is the reference document for LBNE science program and current status. Chapters 1, 3, and 9 provide a comprehensive overview of LBNE's scientific objectives, its place in the landscape of neutrino physics worldwide, the technologies it will incorporate and the capabilities it will possess. 288 pages, 116 figure

SuperCDMS Background Models for Low-Mass Dark Matter Searches

University of Minnesota Ph.D. dissertation.August 2018. Major: Physics. Advisor: Priscilla Cushman. 1 computer file (PDF); xiii, 181 pages.An abundance of astrophysical and cosmological evidence indicates the existence of a non-luminous, non-baryonic form of matter, called dark matter, that is approximately a quarter of all energy in the universe. One promising candidate for dark matter is the Weakly Interacting Massive Particle (WIMP) which interacts with baryonic matter at most on the scale of the weak force. The Cryogenic Dark Matter Search (CDMS) experiment aims to detect the nuclear recoils induced by the elastic scattering of WIMPs off of germanium nuclei. This is a rare signal and difficult to detect, especially the low-energy recoils that are produced by low-mass dark matter. The CDMS project operated at the Soudan Underground Laboratory from 2003--2015, with an upgrade to the SuperCDMS experiment in 2012. The germanium detectors were operated at 50~mK and able to measure both the ionization and athermal phonons produced in a particle interaction. Measuring two signals enables discrimination between electron recoil and nuclear recoil events. An alternative operating mode for the detectors is called the CDMS low ionization threshold experiment (CDMSlite), where a higher bias was applied to the detectors and only the phonon signal analyzed. This method increased sensitivity to low-mass dark matter interactions, but sacrificed discrimination capability. The CDMSlite spectrum had a large contribution from electron recoil background events. From the information gained during the first two CDMSlite Runs, a background model was developed for the third and final CDMSlite Run. Analytical descriptions were identified for those backgrounds that were theoretically known, e.g. tritium $\beta$-spectrum, and Geant simulations were used to understand and predict the low-energy spectra from other sources, e.g. Compton scattering. Multiple new models were developed for detectors operated in CDMSlite at Soudan. These include the analytical formula for Compton scattering, and empirical models for surface backgrounds from $^{210}$Pb contamination of the germanium crystals and detector housing. In order to accurately describe the surface events, a new detector response function was developed that included information about the electric field and energy resolution of the detector. These models were essential to the implementation of a profile likelihood analysis of the CDMSlite Run 3 data, which improved on the sensitivity to dark matter over the Run 2 optimum interval analysis for WIMP masses above 2.5~GeV/$c^2$. This demonstrated a successful application of a likelihood analysis to the high-voltage operating mode, and the potential for these analyses in the future SuperCDMS SNOLAB experiment. For the SuperCDMS SNOLAB experiment, the change in background rates from radiogenic neutrons was considered as additional towers of detectors were added, and the feasibility of an active neutron veto as a potential upgrade for large payloads was studied. This veto could be constructed of plastic scintillator with layers of gadolinium resin, and would aid in reducing the nuclear recoil single scatter background that is indistinguishable from the WIMP signal

A Computational Evaluation Of Neutron Capture Efficiency In Plastic Scintillators

A Monte Carlo study using GEANT4 was performed on the neutron capture efficiency rates achieved by Gd-loaded plastic scintillators. A "deposition efficiency" parameter was defined as the percentage of incident neutrons which were captured in the Gd-loaded scintillator, and whose emitted gammas deposited energy above a certain threshold in a larger layer of plastic scintillator. Deposition efficiency curves were collected for varying thresholds and Gd concentrations, and the results are discussed here.This research was supported by the Undergraduate Research Opportunities Program (UROP)