Physics Commons^™

Impurity Production And Transport In The Prototype Material Plasma Exposure Experiment, Clyde J. Beers

Doctoral Dissertations

The Prototype Material Plasma Exposure eXperiment (Proto-MPEX) is a linear pulse plasma device at Oak Ridge National Laboratory with the purpose of doing the research and development for the heating concepts on the planned full MPEX device. The goal of MPEX is to perform material studies at fusion relevant conditions. To understand the conditions at the material target for performing plasma-material interaction studies the ion temperature and density, the electron temperature and density, and the particle flux and fluence must be known. Impurities within Proto-MPEX can alter the desired conditions at the material target and need to be understood for …

Electroweak Interactions And Fundamental Symmetries In Light Nuclei With Short-Range Effective Field Theories, Zichao Yang

Doctoral Dissertations

Effective field theories(EFTs) are powerful tools to study nuclear systems that display separation of scales. In this dissertation, we present halo EFT results for the $\beta$-delayed proton emission from $^{11}$Be, and pionless EFT results for three-nucleon systems. Halo nuclei are simply described by a tightly bound core and loosely bound valence nucleons. Using the halo EFT, we calculate the rate of the rare decay $^{11}$Be, which is a well-known halo nucleus, into $^{10}\text{Be} + p +e^- + \bar{\nu}_e$. We assume a shallow $1/2 ^+$ resonance in the $^{10}$Be$-p$ system with an energy consistent with a recent experiment by Ayyad {\it …

Search For New Physics In Rare Higgs Boson Decays With The Cms Detector At The Large Hadron Collider, Himal Acharya

Doctoral Dissertations

A new boson with a mass of 125 GeV was discovered at the large hadron collider (LHC) in July 2012. The properties of this particle are so far consistent with the standard model (SM) expectation. Differences in the Higgs boson decay rates and predicted by the SM might indicate the presence of new particles and forces between them. Particularly, rare exclusive decays of the Higgs boson are a promising laboratory to study physics beyond the standard model. Searches for decays of the Higgs boson into a Z boson and a J/ψ meson or into pairs of J/ψ or Υ mesons …

Production Of Protactinium-229 Via Deuteron Irradiation Of Thorium-232, Naser Burahmah

Doctoral Dissertations

²²⁵Ac [Actinium-225] is a promising radionuclide for targeted alpha therapy of cancer. ²²⁹Pa can lead to the production of ²²⁹Th [Thorium-229] and ²²⁵Ac [Actinium-225]. Deuteron bombardment on natural thorium targets has been investigated to measure cross sections of protactinium isotopes. In this work, ²²⁹Pa [Protactinium-229] excitation function was measured via deuteron energies up to 50 MeV [Mega electron volt] of thin thorium foils. The irradiation took place at Lawrence Berkeley National Laboratory’s (LBNL) 88-Inch Cyclotron. The target processing and analysis were performed at Oak Ridge National Laboratory (ORNL). The target consisted of 4 thin foils …

A Search For Exotic Higgs Decays Or: How I Learned To Stop Worrying And Love Long-Lived Particles, Jackson Burzynski

Doctoral Dissertations

A novel search for exotic decays of the Higgs boson to pairs of long-lived neutral particles, each decaying to a bottom quark pair, is performed using 139 fb^-1 of sqrt{s} = 13 TeV proton-proton collision data collected with the ATLAS detector at the LHC. Events consistent with the production of a Higgs boson in association with a leptonically-decaying Z boson are analyzed. Long-lived particle (LLP) decays are reconstructed from inner detector tracks as displaced vertices with high mass and track multiplicity relative to Standard Model processes. The analysis selection requires the presence of at least two displaced vertices, effectively …

Pattern Formation And Phase Transition Of Connectivity In Two Dimensions, Arman Mohseni Kabir

Doctoral Dissertations

This dissertation is devoted to the study and analysis of different types of emergent behavior in physical systems. Emergence is a phenomenon that has fascinated researchers from various fields of science and engineering. From the emergence of global pandemics to the formation of reaction-diffusion patterns, the main feature that connects all these diverse systems is the appearance of a complex global structure as a result of collective interactions of simple underlying components. This dissertation will focus on two types of emergence in physical systems: emergence of long-range connectivity in networks and emergence and analysis of complex patterns. The most prominent …

Search For Resonant Pair Production Of Higgs Bosons In The Four B-Quark Final State With The Atlas Detector, Dale Abbott

Doctoral Dissertations

A search for heavy resonances decaying to Higgs boson pairs in the $b\overline{b}b\overline{b}$ final state with 139 $fb^{-1}$ of LHC proton-proton (pp) collision data collected at $\sqrt{s} = 13$ TeV obtained by the ATLAS detector during the 2015-2018 time period. Two benchmark signals are studied, both of which decay into a Higgs boson pair: a spin-2 Kaluza-Klein Graviton and a scalar resonance. This thesis studies high transverse momentum (boosted) resonances, which range from 900-5000 GeV. No statistically significant excesses are observed and the results are found to be compatible with the Standard Model. Upper limits are set on the production …

An Experimental Study Of Lipid-Membrane Based Structure Formation And Development Of A Responsive System, Rui Cao

Doctoral Dissertations

This thesis shows how controlling adhesive interactions among lipid bilayer vesicles and surrounding polymers or particles leads to formation of new mesoscopic and macroscopic structures. The vesicle-gel reported could find application as a closed-cell, 99% water solid platform for releasing cargo in response to a stimulus, either by tuning membrane permeability or by disruption of the vesicles.

In Situ Cosmogenic Backgrounds In The Majorana Demonstrator, Andrew Lopez

Doctoral Dissertations

Neutrino-less double-beta decay is a proposed type of radioactive decay that, if observed, could answer several outstanding physics questions, such as "Is the neutrino its own antiparticle otherwise known as a Majorana particle?", "What is the mass of the neutrino?", and "What is the neutrino mass hierarchy?" As technology and experimental techniques improve, the sensitivity of experiments looking for rare events becomes more dependent on the backgrounds. Some of these backgrounds can be reduced using shielding techniques such as implementing a veto system, selecting radiopure components, and conducting the experiment deep underground. However some amount of cosmogenically induced backgrounds remain …

Fabrication Of Specialized Scintillators For Nuclear Security Applications, Cordell James Delzer

Doctoral Dissertations

Radiation detectors are important for a variety of fields including medical imaging, oil drilling, and nuclear security. Within nuclear security, they can serve a multitude of purposes whether that be imaging, localization, isotopic identification, or even just activity measurement. Even without directly seeing a nuclear material it is often able to notice their existence without a detector. Scintillators make up an important part of these detectors due to their large intrinsic efficiency, low cost, large volume, and relatively low upkeep. Due to the importance of the large number of purposes these scintillators may be used for, it can often be …

Neutron Star Structure From Electromagnetic And Gravitational Wave Observations, Mohammad Al-Mamun

Doctoral Dissertations

Neutron star (NS) research primarily relied on spectral observations before the first gravitational wave (GW) detection from the binary neutron star merger was done by the LIGO-VIRGO collaboration. The GW170817 merger event provided mass and tidal deformability Λ˜ constraints for neutron stars. This project used these constraints and associated them with the constraints made by the NS X-ray observations to construct neutron star models. Selective X-ray sources were used in this work, which showed reliable uncertainties from their previous uses. The mass-radius constraints from the electromagnetic (EM) observations were constructed from seven quiescent low-mass X-ray binaries (QLMXBs), three photospheric radius …

Roughening Interfaces In Spatial Population Dynamics, Clarisa E. Castillo

Doctoral Dissertations

The spatial structure and geometry of biological systems can have a strong effect on that system’s evolutionary dynamics. In particular, spatially structured populations may invade one another, giving rise to invasion fronts that may exhibit qualitatively different evolutionary dynamics in different dimensions or geometric configurations. For examples of invasion fronts arising in nature, one might think of a thin layer of bacteria cells growing on a Petri dish, an animal species expanding into new territory, or a cancerous tumor growing into and competing with the surrounding healthy tissue. Perhaps the most well-studied class of invasion fronts in population genetics is …

A Study Of Systematic Uncertainties For A Photon-Like Low Energy Excess Search At Microboone, Gray Yarbrough

Doctoral Dissertations

The premise of this dissertation is the study of and reduction of systematic uncertainties in the MicroBooNE experiment at the Fermi National Accelerator Laboratory. MicroBooNE is a short-baseline oscillation experiment using the innovative liquid argon time projection chamber technology to study, with unprecedented detail, neutrino interactions. The primary goal of MicroBooNE is the investigation of the MiniBooNE low energy excess (LEE) of electron neutrino events, a result which raised fundamental questions on the existence of sterile neutrinos with broad implications to the field of particle physics. The principal study of this dissertation is a study of systematics as part of …

Collector Probe Measurements Of Sol Impurity Accumulation And The Implications Of Sol Flows On The Accumulation Amount, Shawn Zamperini

Doctoral Dissertations

A collector probe in its simplest form is a rod inserted into a plasma so that impurities are deposited onto it. These probes are then removed and analyzed to determine the deposition profile both along the length of probe and across the width of it. This dissertation covers a series of collector probes experiments and accompanying interpretive modelling all with the main goal of providing evidence for long-hypothesized near scrape-off layer (SOL) accumulation of impurities that can lead to efficient core contamination. The structure of this dissertation is as follows. A brief outline of fusion energy and why we need …

Population Annealing: Analysis, Optimization And Application To Glassy Systems, Christopher A. Amey

Doctoral Dissertations

Glasses are physical systems that lack structural order and exhibit extremely slow dynamics, which makes them challenging to study. In this thesis we apply Monte Carlo methods to two distinct glassy systems: the 3D Edwards-Anderson spin glass and a binary hard sphere fluid. While significant progress has been made on theoretical and experimental fronts, much of our current understanding of glasses has come from numerical simulations. Standard Monte Carlo techniques cannot be used to perform equilibrium simulations due to slow dynamics in the glassy regime. As a result, several specialized techniques have been developed in order to simulate such systems, …

Local Dynamics And Atomic-Level Structures In Metallic Liquids And Glasses, Zengquan Wang

Doctoral Dissertations

Structure and dynamics at the atomic level in metallic glasses and liquids are poorly understood when compared to the crystalline solids. For instance, even though viscosity is the basic property of liquids, its atomistic origin is not well elucidated. Also, the physics of the fragility of liquids and the crossover phenomenon is far from full understanding. Earlier, through molecular dynamics (MD) simulations a direct connection was found between the timescale describing the macroscopic viscous behavior, the Maxwell relaxation time (t_M = h/G_∞, h is the shear viscosity and G_∞ is the high-frequency shear modulus) and …

Towards Neutron Transformation Searches, Joshua L. Barrow

Doctoral Dissertations

To probe the origins of the baryon asymmetry, baryon number violation, the last unconfirmed Sakharov condition, must be definitively observed experimentally. Similarly, the nature of dark matter is currently unknown, and calls out for new candidates to be investigated. Each of these issues can be considered through the study of neutron transformations.

Some rare baryon number violating processes, such as neutron-antineutron transformations, are expected to probe baryogenesis. Here, I show progress on this discovery target through construction of more accurate Monte Carlo models, the design of future detectors, creation of more complete atmospheric neutrino background simulations, and use of automated …

Spectroscopic Properties Of Ferroic Superlattices, Shiyu Fan

Doctoral Dissertations

The interplay between charge, structure, magnetism, and orbitals leads to rich physics and exotic cross-coupling in multifunctional materials. Superlattices provide a superb platform to study the complex interactions between different degrees of freedom. In this dissertation, I present a spectroscopic investigation of natural and engineered superlattices including Fe_xTaS₂ and (LuFeO₃)_m/(LuFe₂O₄)₁ under external stimuli of temperature and magnetic field as well as chemical substitution. Studying the phase transitions, symmetry-breaking, and complex interface interactions from a microscopic viewpoint enhances fundamental understanding of coupling mechanism between different order parameters and the …

Characterization And Benchmarking Of Quantum Computers, Megan L. Dahlhauser

Doctoral Dissertations

Quantum computers are a promising technology expected to provide substantial speedups to important computational problems, but modern quantum devices are imperfect and prone to noise. In order to program and debug quantum computers as well as monitor progress towards more advanced devices, we must characterize their dynamics and benchmark their performance. Characterization methods vary in measured quantities and computational requirements, and their accuracy in describing arbitrary quantum devices in an arbitrary context is not guaranteed. The leading techniques for characterization are based on fine-grain physical models that are typically accurate but computationally expensive. This raises the question of how to …

Numerical Studies Of Superconductivity And Charge-Density-Waves: Progress On The 2d Holstein Model And A Superconductor-Metal Bilayer, Philip M. Dee

Doctoral Dissertations

The problem of superconductivity has been central in many areas of condensed matter physics for over 100 years. Despite this long history, there is still no theory capable of describing both conventional and unconventional superconductors. Recent experimental observations such as the dilute superconductivity in SrTiO₃ and near room-temperature superconductivity in hydride compounds under extreme pressure have renewed interest in electron-phonon systems. Adding to this is evidence that electron-phonon coupling may play a supporting role in unconventional systems like the cuprates and monolayer FeSe on SrTiO₃.

One way to make sense of these observations is to construct simple …

Measuring Electron Diffusion And Constraining The Neutral Current Π0 Background For Single-Photon Events In Microboone, Andrew Mogan

Doctoral Dissertations

Liquid Argon Time Projection Chambers (LArTPCs) are a rising technology in the field of experimental neutrino physics. LArTPCs use ionization electrons and scintillation light to reconstruct neutrino interactions with exceptional calorimetric and position resolution capabilities. Here, I present two analyses conducted in the MicroBooNE LArTPC at Fermilab: a measurement of the longitudinal electron diffusion coefficient, DL, in the MicroBooNE detector and a constraint of the systematic uncertainty on MicroBooNE's single-photon analysis due to the dominant neutral current (NC) π0 background. Longitudinal electron diffusion modifies the spatial and timing resolution of the detector, and measuring it will help correct for these …

Synthetic Heterosynaptic Plasticity Enhances The Versatility Of Memristive Systems Emulating Bio-Synapse Structure And Function, William T. Mcclintic

Doctoral Dissertations

Memristive systems occur in nature and are hallmarked via pinched hysteresis, the difference in the forward and reverse pathways for a given phenomenon. For example, neurons of the human brain are composed of synapses which apply the properties of memristance for neuronal communication, learning, and memory consolidation. Modern technology has much to gain from the characteristics of memristive systems, including lower power operation, on-chip memory, and bio-inspired computing. What is more, a relationship between memristive systems and synaptic plasticity exists and can be investigated focusing on homosynaptic and heterosynaptic plasticity. Where homosynaptic plasticity applies to interactions between neurons at a …

Study Of 134in Beta-Delayed Neutron Emission And Development Of A New Generation Neutron Detector, Joseph Heideman

Doctoral Dissertations

Beta-delayed neutron emission in very neutron-rich nuclei plays an essential role in nuclear structure and the understanding of the astrophysical r-process. A complete description of this process requires knowledge of both steps, beta decay and neutron emission. A leading theory poses the intermediate daughter nucleus to behave as a compound nucleus. The conditions for beta-delayed neutron emission of 134In are not well described by the assumptions in the neutron pandemonium hypothesis, therein providing a unique case to this process due to the proximity to 132Sn. Single-particle states in 133Sn obvserved after neutron emission have dissimilar shell occupancy compared to neutron-hole …

Multi-Scale Computational Modeling Of Metal/Ceramic Interfaces, Abu Shama Mohammad Miraz

Doctoral Dissertations

Multi-scale atomistic calculations were carried out to understand the interfacial features that dictate the mechanical integrity of the metal/ceramic nanolaminates. As such, first principles density functional theory (DFT) calculations were performed to understand the electronic and atomistic factors governing adhesion and resistance to shear for simple metal/ceramic interfaces, whereas molecular dynamics (MD) simulations were performed to observe the impact of interfacial structures, such as misfit dislocation network geometries and orientation relationships, on interfacial mechanical properties.

For the DFT investigation, we choose metals with different crystal structures, namely - Cu (fcc), Cr (bcc) and Ti (hcp) along with a variety of …

A Search For New Resonances Decaying Into A Weak Vector Boson And A Higgs Boson In Hadronic Final States With The Atlas Detector At The Large Hadron Collider, Zachary Alden Meadows

Doctoral Dissertations

A search for heavy resonances decaying to a $W$ or $Z$ boson and a Higgs boson in the final state is described. The search uses $139\ \mathrm{fb}^{-1}$ of proton-proton collision data at $\sqrt{s} = 13$ TeV collected by the ATLAS detector at the CERN Large Hadron Collider from 2015 to 2018. The results are presented in terms of constraints on a simplified model with a heavy vector triplet. Upper limits are set on the production cross-section times branching fraction for resonances decaying into a W/Z boson and a Higgs boson in the mass range between 1.2 to 5 TeV.

Improving The Data Quality In Gravitation-Wave Detectors By Mitigating Transient Noise Artifacts, Kentaro Mogushi

Doctoral Dissertations

“The existence of gravitational waves (GWs), small perturbations in spacetime produced by accelerating massive objects was first predicted in 1916 as solutions of Einstein’s Theory of General Relativity (Einstein, 1916). Detecting and analyzing GWs produced by sources allows us to probe astrophysical phenomena.

The era of GW astronomy began from the first direct detection of the coalescence of a binary black hole in 2015 by the collaboration of the advanced Laser Interferometer Gravitational-wave Observatory (LIGO) (Aasi et al., 2015) and advanced Virgo (Abbott et al., 2016a). Since 2015, LIGO-Virgo detected about 50 confident transient events of GW signals (Abbott et …

Critical Behavior In Evolutionary And Population Dynamics, Stephen Walter Ordway

Doctoral Dissertations

“This study is an exploration of phase transition behavior in evolutionary and population dynamics, and techniques for predicting population changes, across the disciplines of physics, biology, and computer science. Under the looming threat of climate change, it is imperative to understand the dynamics of populations under environmental stress and to identify early warning signals of population decline. These issues are explored here in (1) a computational model of evolutionary dynamics, (2) an experimental system of decaying populations under environmental stress, and (3) a machine learning approach to predict population changes based on environmental factors. Through the lens of critical phase …

Fiber Optic Sensors For Industry And Military Applications, Yiyang Zhuang

Doctoral Dissertations

"Fiber optic sensors (FOSs) have been widely used for measuring various physical and chemical measurands owing to their unique advantages over traditional sensors such as small size, high resolution, distributed sensing capabilities, and immunity to electromagnetic interference. This dissertation focuses on the development of robust FOSs with ultrahigh sensitivity and their applications in industry and military areas.

Firstly, novel fiber-optic extrinsic Fabry-Perot interferometer (EFPI) inclinometers for one- and two-dimensional tilt measurements with 20 nrad resolution were demonstrated. Compared to in-line fiber optic inclinometers, an extrinsic sensing motif was used in our prototype inclinometer. The variations in tilt angle of the …

Computational Studies Of Carbon Nanocluster Solidification, Chathuri Chandani Silva

Doctoral Dissertations

“A subset of micron-size meteoritic carbon particles formed in red giant atmospheres show a core-rim structure, likely condensed from a vapor phase into super-cooled carbon droplets that nucleated graphene sheets (~40Å) on randomly oriented 5-atom loops during solidification, followed by coating with a graphite rim. Similar particles form during slow cooling of carbon vapor in the lab.

Here we investigate the nucleation and growth of carbon rings and graphene sheets using density functional theory (DFT). Our objectives: (1). explore different computational techniques in DFT-VASP for various carbon structures and compare the results with literature, (2). investigate the nucleation and growth …

Complete Experiments On Multi-Photon Ionizations Of Ultra-Cold And Polarized Atoms, Bishnu Prasad Acharya

Doctoral Dissertations

“Fundamental atomic processes such as collision-induced ionization are of relevance in many scientific fields. Describing these reactions can still pose a substantial challenge due to the well-known “few-body problem”, which entails that there is no analytical solution of the equations of motion for systems of more the 2 mutually interacting particle. Novel experimental tools and advancements in theorical methods enable to obtain detailed information on atomic dynamics providing insight into both, the phase as well as the amplitude of the quantum-mechanical wave functions of the particles. In this project, we developed experimental techniques studying multi-photon ionization of lithium in femto-second …