Ph.D. - Physics
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Item DNN-based NMR Artifact Correction Method(2024) Nam, Sejin; Browder, Thomas TB; PhysicsItem Direct Dark Matter Search with the DarkSide Experiment(2024) Goicoechea Casanueva, Víctor; Maricic, Jelena; PhysicsItem NTC, NuLat, and miniTimeCube: The Development of Compact, Mobile, Neutral Particle Detectors(2019) Dorrill, Ryan Christopher; Learned, John G.; PhysicsItem Multiclass Search for Cosmic Ultra-High Energy Neutrinos with ANITA-IV(University of Hawaii at Manoa, 2023) Russell, John Walsh; Learned, John G.; PhysicsThe Antarctic Impulsive Transient Antenna (ANITA) is a balloon-borne experiment that suspends over the Antarctic ice sheet to detect upcoming radio pulses. Its goal is to see radio pulses originating from a rare interaction between Ultra-High Energy (UHE) neutrinos and ice to produce a shower of charged particles. The electromagnetic radiation produced from this shower is known as Askaryan radiation. The sensitivity at which ANITA needs to detect these events means most of the data ANITA collects is background. This background comes from multiple sources, from natural sources like the sun and electromagnetic discharge aboard the instrumentation to anthropogenic sources like satellites and research base communication. Also collected by ANITA are signals associated with radiation from charged particle showers produced in the air interacting with the Earth's magnetic field. In contrast to the radio pulses in the ice that are expected to be vertically polarized, these events are found to be horizontally polarized. Past analyses have focused on designing final cuts to remove thermal background, considering it to dominate over other types of background. However, after selecting events that look most like signals of interest, I estimate an upper limit to how many of them could be misclassified background. My exploratory analysis found 33 events, with 32 estimated as belonging to classes with horizontal polarization and one with vertical polarization.Item Development of Digital Architectures for Pixelated Readout of Time Projection Chambers: Q-Pix(University of Hawaii at Manoa, 2023) Keefe, Kevin; Nishimura, Kurtis; PhysicsThe Standard Model (SM) of physics has proven successful over the past decades, despite several measurements that indicate its incomplete description of nature.The search for New Physics (NP) continues at higher energies with larger detectors. One such future detector is the Deep Underground Neutrino Experiment (DUNE). DUNE is a combination of two detectors, a near detector (ND) and a far detector (FD), which will be used together to search for Charge-Parity Violations (CPV) in the lepton sector. The DUNE FD will be a combination of four large ($\approx$~10~\unit{kT}) Liquid Argon Time Projection Chambers (LArTPC). Each 10-kT FD requires high precision in both time ($\le~1~\mu s$) and spatial resolution ($\approx$~1~\unit{mm}) for vertex reconstruction and particle identification (PID) of neutrino events. This dissertation discusses the progress and characterization of a novel implementation of a new pixelated LArTPC readout technology that can be used in an FD.This novel readout is based on a pixel-level charge-integrate-reset circuit: Q-Pix. We present the basic pixel-level readout circuit and the implications of such an implementation when used in kiloton LArTPCs. We also show results from the first prototype implementation based on the Q-Pix readout, which was designed using only off-the-shelf electronics. One problem with any pixelated readout is the ability to handle a large number of unique data channels, which in the case of the DUNE-FD is $\approx 10^8$.To address the scaling problem, we have developed and tested a modular digital back-end prototype as a proof of concept. This prototype is based on the first Q-Pix digital ASIC design also presented in this thesis. We discuss the back-end system requirements for a Q-Pix based readout technology to provide neutrino oscillation measurements up to 10~\unit{GeV}, and present the first demonstration of local oscillator calibrations ($\sim$~0.1~\unit{ppm}). Simulations were performed based on radiogenic backgrounds and high-energy neutrino beam line events, providing first constraints on digital back-end requirements in both the quiescent and active states. Finally, based on these results from the simulations and prototypes presented here, we discuss the digital back-end readout of a fully realized Q-Pix implementation within a 10~\unit{kT} DUNE-FD module.Item Low-Energy Physics in Liquid Argon Time Projection Chambers(University of Hawaii at Manoa, 2023) Dvornikov, Olexiy; Maricic, Jelena; PhysicsThe Deep Underground Neutrino Experiment (DUNE) will be at the frontier of neutrino physics. However, its goals require unprecedented calibrations of charge, light readout, and the detector electric field. Especially for the subcomponents exposed to an intense neutrino beam. Particles traversing liquid argon time projection chambers (LArTPCs) leave behind wakes of ionization electrons. DUNE, whose main components are LArTPCs, will image the topologies of these wakes with ~ 0.5 cm precision and ~500 ns timing resolution and, based on the kinematics, identify the particle species and interaction types. In other words, DUNE will conduct precision neutrino physics. This thesis is a calibration and a study of ~ 10 - 100 MeV electromagnetic interactions in LArTPCs. Although DUNE will be sensitive to a wide range of energies, this work focuses on the low end. Also, this thesis is a calibration of LArTPC electric fields. At the MeV scale, DUNE will be sensitive to solar, supernova, and perhaps even exotic neutrinos. However, this sensitivity rests squarely on detector calibrations. This thesis examines ~ 10 MeV and 236 MeV with measured delta-rays and simulated anomalous kaon decay-at-rest (KDAR) neutrinos respectively. I show that the ~ 10 MeV response differs from predictions by < 10%. This is very encouraging for neutrino astronomy. I also show that DUNE will be sensitive to very low anomalous neutrino fluxes from the Sun. This is exciting for testing dark matter models which can be linked to neutrinos. This work also measures the spatial offsets (at the ~ mm level) due to electric field distortions in DUNE prototypes, highlighting possible defects and the need for meticulous field characterization for future LArTPCs.Item Light nuclei and antinuclei production in proton-proton interactions(University of Hawaii at Manoa, 2023) Shukla, Anirvan; Von Doetinchem, Philip; PhysicsIdentifying the nature of dark matter is a major unsolved problem in physics. The detection of low-energy cosmic-ray antinuclei could provide a "smoking gun" signature of dark matter annihilation or decay, as they are produced essentially free of the astrophysical background. Such a detection could also indicate new astrophysical phenomena like undiscovered antimatter sources in our Galaxy. The main source of astrophysical antinuclei background are the interactions of cosmic-ray protons with hydrogen in the thin interstellar gas. However, their formation process is poorly understood. The impact of new-physics searches with cosmic-ray antinuclei can be increased by reducing uncertainties related to antinuclei formation modeling. For that purpose, this dissertation discusses how the coalescence mechanism for (anti)deuterons was extended to estimate the production of antihelium in cosmic-ray interactions. The results were used to model how antinuclei are transported in our Galaxy, to predict the antinuclei flux received at Earth. The production mechanism of light antinuclei have been studied in accelerator-based experiments before. However, very few proton-proton measurements exist at energies which are relevant for cosmic-ray antinuclei production. Modeling of antinuclei formation also requires high-precision measurements of antiproton production. These factors motivate the analysis of new large p-p data sets from modern particle accelerator experiments. NA61/SHINE is a fixed-target experiment at the CERN-SPS, which studies hadron-nucleus and nucleus-nucleus collisions for various physics goals. This dissertation presents new measurements of proton, antiproton, as well as pion and kaon spectra, using the high-statistics p-p data from NA61/SHINE. The new results significantly extend the phase space coverage in rapidity and transverse momentum, as compared to previous results. They also dramatically reduce uncertainties in antiproton production. The first measurements of deuteron production at energies relevant for cosmic-ray studies are presented. The viability of measuring antideuteron production and two-particle angular correlations, with the recently-upgraded NA61/SHINE detector, is also shown.Item Topics on Dark Matter and Active Galactic Nuclei(University of Hawaii at Manoa, 2022) Runburg, Jack; Kumar, Jason; Farrah, Duncan; PhysicsDespite gravitational evidence at many spatial scales and significant experimental efforts, non-gravitational detection of dark matter has thus far been unsuccessful.Indirect dark matter detection, one of several strategies to find confirmation of the existence of dark matter and untangle its properties, aims to identify dark matter through its self-annihilation products. In particular, self-annihilation processes of thermal relic dark matter candidates (WIMPs) may produce gamma rays, providing a potentially observable signature of dark matter. After 'freezing out' of thermal equilibrium, hierarchical structure formation in cold dark matter models produces abundant `halos' and 'subhalos' of gravitationally bound dark matter clumps that host the galaxies and clusters we see today. Depending on their size and history, these halos are characterized by different dark matter velocity scales, suppressing or enhancing annihilation rates depending on the velocity-dependence of the cross section. This dissertation considers the prospects of detecting dark matter with a velocity-dependent self-annihilation cross section in dwarf spheroidal galaxies, extragalactic halos, the Milky Way center, and in galactic substructure. We will find that the angular distribution of gamma rays from dark matter annihilation and the overall normalization of the flux are sensitive to both the microphysics and the astrophysical distribution of the dark matter. A key challenge in all of these analyses are the considerations of gamma ray backgrounds from other astrophysical sources. Blazars, star-forming galaxies, and cosmic rays all contribute to gamma ray fore-/backgrounds. Without better understanding and modelling of these sources, indirect searches for dark matter are going to be stymied. The luminosity function (LF) of active galactic nuclei (AGN) describes the population of AGN as a function of redshift and luminosity. Estimates of gamma ray backgrounds from unresolved AGN can be obtained from the faint end of the AGN LF. Towards this goal, this dissertation presents the AGN LF constructed using midinfrared and X-ray data in the XMM-LSS field. I close with discussions on how AGN LFs can be used to model gamma ray backgrounds in indirect detection analyses and how newer machine learning methods may overcome some of the challenges of both current AGN LF analyses and dark matter searches.Item Unusual Near-Horizon Cosmic-Ray-Like Events Observed by the Fourth Flight of ANITA(University of Hawaii at Manoa, 2022) Prechelt, Remy; Gorham, Peter W.; PhysicsDespite decades of experimental observations, the astrophysical sources producing the measured flux of ultrahigh energy cosmic rays (UHECRs) have yet to be identified. Neutrinos, extremely weakly interacting neutral particles, are expected to be produced inside the astrophysical accelerators responsible for the production of UHECRs, and during the propagation of UHECRs to Earth. As neutral weakly-interacting particles, ultrahigh energy neutrinos are perhaps the best probe of the hadronic and leptonic processes governing these extreme astrophysical environments beyond the local universe. Yet, despite two decades of experimental searches, ultrahigh energy neutrinos have never been definitively detected. ANITA-IV, the fourth flight of the ANtarctic Impulsive Transient Antenna (ANITA), observed four anomalous events extremely close to the horizon. In this dissertation, I present the possibility that one or more of these anomalous “near horizon” events are indeed ultrahigh energy tau neutrinos detected via the unique Earth-skimming “tau air shower channel”. I develop the first “end-to-end” simulation of ANITA-IV’s sensitivity to these unique events and I use this simulation to determine whether these events are observationally consistent with tau-lepton-induced extensive air showers and, if they are, what are the constraints on the implied flux from populations of diffuse and point-like neutrino sources. Finally, I perform a blind search for any statistically significant associations between these four anomalous events and catalogs of astrophysical sources that are considered to be possible ultrahigh-energy neutrino and cosmic ray emitters. I find that these events are not observationally inconsistent with ultrahigh energy tau neutrinos, but that the implied (diffuse) flux and (point-like) fluence necessary to explain these events is in strong tension with limits set by other observatories, such as the Pierre Auger Observatory and IceCube. After unblinding the results of my search for associations between these events and catalogs of sources that have the potential to be UHECR sources, I find no statistically significant associations with any of the considered sources.Item From neutrons to dark matter: Directional recoil detection and utilization of deep learning for gaseous time projection chambers(University of Hawaii at Manoa, 2022) Schueler, Jeffrey Thomas; Vahsen, Sven E.; PhysicsModern gaseous time projection chambers (TPCs) with high readout segmentation are capable of reconstructing detailed 3D ionization distributions with voxel sizes of order (\SI{100}{\um})$^3$. This enables measurements of the 3D momentum vectors of short, mm-scale nuclear recoils, which is of interest for neutron measurements, as well as searches for dark matter, where directionality opens the possibility of identifying the galactic origin of weakly interacting massive particles (WIMPs), even below the so-called neutrino floor. We perform a variety of experiments and simulations with eight miniature TPCs filled with a 70:30 mixture of He:CO$_2$ gas at \SI{1}{atm} pressure. Each so-called BEAST TPC is of identical design and contains two gas electron multiplier (GEM) amplification devices and a $(2.00\times 1.68)~\text{cm}^2$ pixel-ASIC readout. We first detail the measurement of neutron backgrounds at the SuperKEKB $e^+e^-$ collider in Tsukuba Japan. We focus on measurements surrounding SuperKEKB's final focusing magnets (recorded in 2018) and in the accelerator tunnel surrounding the Belle II detector (recorded in 2020-2021). In our analyses we reject large X-ray backgrounds from the accelerator, resulting in $>$99$\%$ pure samples of nuclear recoils down to recoil energies as low as \SI{8.0}{keV_{ee}}. We find excellent agreement between measured and simulated nuclear recoil energy spectra indicating that our simulations model neutron production well. We additionally introduce a correction for charge integration bias in observed recoil tracks with high axial inclination. This correction leads to correct vector directional ``head-tail" (sign of 3D vector) assignment for $91\%$ of simulated He recoils ranging from $\SI{40}{keV_{ee}}$ to about $\SI{1}{MeV_{ee}}$, with a mean angular resolution of 8$^\circ$; a significant improvement over the $72\%$ head-tail efficiency achieved without these corrections. Applying this technique to measurement leads to an agreement between measured and simulated angular distributions that allows us to conclude the existence of a neutron production hotspot in the accelerator tunnel. While the BEAST TPCs are highly sensitive to ionization, and can detect even single electrons, extending directionality to the keV-scale, as is desirable for dark matter searches, requires operating the detectors with lower-density gases, at higher gains, and developing improved analysis techniques. We here focus on the two latter aspects. We improve on existing head-tail classification methods through the introduction of deep-learning computer-vision algorithms called 3D convolutional neural networks (3DCNNs). We first perform a simulation benchmark study where we train a 3DCNN to assign directional head-tail to simulated neutron recoils with energies up to \SI{515}{keV_r} and compare these results to three existing methods of head-tail assignment. We find a head-tail efficiency of $99.9\%$ on this sample using the 3DCNN, compared to $97.8\%$, $93.7\%$, and $79.0\%$ for existing methods. Next, we measure neutrons from a $^{252}$Cf source incident on separate sides of a TPC. We operate both at low gain and high gain. At low gain, the simulation-trained 3DCNN reliably identifies whether the observed recoil points toward or away from the $^{252}$Cf source. On a small sample of identified He recoils between \SI{39}{keV_{ee}} and \SI{49}{keV_{ee}}, before correcting for residual background such as back-scattered events, we observe a head-tail efficiency of $(62.1\pm 11.4)\%$. Using simulation, we show that the true head-tail efficiency after correcting for residual backgrounds should be greater than this, marking the first statistically significant observation of event-level head-tail sensitivity below \SI{50}{keV_{ee}}. At high gain, we attempt to improve our head-tail sensitivity to sub-10-$\rm keV_r$ recoils, and also introduce a 3DCNN for event identification. In simulation, we reject all X-ray backgrounds down to \SI{5}{keV_{ee}} at $50\%$ nuclear recoil selection efficiency and demonstrate head-tail efficiencies above $50\%$ for He recoils down to \SI{3}{keV_r}. These results do not yet generalize to measurement, which is currently being investigated. If the 3DCNN robustness can be improved, this would be the first demonstration of directional recoil detection at energies relevant for the directional detection of $\mathcal{O}(\text{GeV})$ dark matter particles. Finally, we perform a study comparing the keV-scale electron background rejection performance of a 3DCNN to the traditional discriminant of track length, as well as discriminants obtained from state-of-the-art shallow learning methods in a simulated detector with an 80:10:10 mixture of He:CF$_4$:CHF$_3$ at \SI{60}{torr}. We train the 3DCNN classifier using recoil charge distributions with ionization energies ranging from 0.5-\SI{10.5}{keV_{ee}} after \SI{25}{cm} of drift. The charges are initially segmented into (\SI{100}{\um})$^3$ bins when determining track length and the shallow learning discriminants, but are rebinned with a reduced segmentation of (\SI{850}{\um})$^3$ for the 3DCNN. Despite the courser binning, compared to using track length, we find that classifying events with the 3DCNN reduces electron backgrounds by an additional factor of up to 1,000 and effectively reduces the energy threshold of our simulated TPC by $30\%$ for fluorine recoils and $50\%$ for helium recoils. We also find that the 3DCNN reduces electron backgrounds by up to a factor of 20 compared to the shallow machine learning approaches, corresponding to a \SI{2}{keV_{ee}} reduction in the energy threshold. Collectively, the results in this thesis highlight the unique measurements enabled by high-resolution ionization imaging, and how 3D convolutional neural networks appear ideally suited to maximally utilize the rich 3D data from detectors with this capability.