Browsing by Subject "dark matter"

Now showing 1 - 6 of 6
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    A Computational Evaluation Of Neutron Capture Efficiency In Plastic Scintillators
    (2016-10-05) Schmitz, Ryan; Poehlmann, David-Michael; Rogers, Hannah; Barker, D'Ann; Cushman, Priscilla
    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.
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    Dark Matter Models in Non-Supersymmetric SO(10) Unification Models
    (2017-06) Zheng, Jiaming
    This thesis studies systematically non-supersymmetric models that contain dark matter candidates. The stability of the dark matter is guaranteed by a remnant Z 2 symmetry embedded naturally in SO(10). We build models base on various dark matter production mechanism, including the non-equilibrium thermal dark matter scenario, the weakly interactive massive particle scenario, and the asymmetric dark matter scenario. Although we start from very general assumptions on the choice of dark matter representation and the symmetry breaking pattern, the number of viable models is severely restricted by the requirement of gauge coupling unification. These models are then checked against several phenomenological constraints, such as the light neutrino masses, direct detection bounds on dark matter candidates and the proton decay lifetime. Finally, we demonstrate that the vacuum stability problem of the Standard Model can be evaded by one of our scalar dark matter models.
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    Searches for Dark Matter production in two fixed target experiments: HPS and LDMX
    (2025-01) Eichlersmith, Tom
    Astrophysical evidence strongly indicates the presence of particulate Dark Matter (DM) within our universe; however, the specific particle nature of DM is still unknown. The wide variety of possible DM particles produces a similar range of experiments focused on probing these different categories of possible DM. This work describes two experiments taking different approaches to search for Light DM residing in the 2MeV-1GeV mass range being produced by electron interactions. The Light Dark Matter eXperiment (LDMX) is a proposed fixed target experiment designed for a missing momentum search with an additional, orthogonal missing energy search channel described here. The Heavy Photon Search experiment (HPS) is another fixed target experiment designed for a displaced vertex search with distances of O(10cm) which are not probed by longer baseline experiments. Specifically, a search in HPS data for a specific Light DM model with a strongly-coupled dark sector enabling a higher expected production rate while keeping the characteristic decay length within HPS's acceptance is also presented.
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    SuperCDMS Background Models for Low-Mass Dark Matter Searches
    (2018-08) Barker, D'Ann
    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.
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    Using Machine Learning to Hunt for Simulated WIMPs in the NOvA Near Detector
    (2023-11) Myers, Dalton
    A neural network was trained on simulated data that included events in which electrons were scattered by hypothetical Dark Matter particles (χ) of mass mχ = 30 MeV assuming a dark vector portal mechanism of a dark photon (A') with mass mA' = 90 MeV, a gauge coupling parameter αD = 1/2, and kinetic mixing parameter e = 2 × 10 -5. The NOvA Near Detector’s response to these events was then simulated, and the pixelmaps (images) of these events occurring within the NOvA Near Detector were then used to train a machine learning algorithm designed to differentiate between the each of the ordinary observed event types that involve an electron scattered by a neutrino and hypothetical events in which an electron was scattered by a dark matter particle.