In recent decades, the accessibility of nuclear physics has been greatly improved due to the advent of modern supercomputers, as well as theoretical developments in effective field theory and ab initio (first--principles) nuclear approaches. As a result, in modern nuclear theory it is possible to perform realistic quantum many--body calculations of nuclear systems, beginning solely from underlying Standard Model symmetries. A fundamental object of interest in nuclear structure are the nuclear densities, which may be abundantly used in calculation of other nuclear observables. Utilizing the ab initio no--core shell model, a rigorous theoretical approach for calculations involving light--nuclei, we study the coordinate space densities of various nuclear systems and discuss the importance of nonlocality and translation invariance in the densities. In particular, this property is investigated at length in the context of scattering theory, in which optical potentials are constructed from the ab initio no--core shell model densities. We explore the impacts of nonlocality and translation invariance in proton and antiproton scattering, and in the latter we review the first fully microscopic optical potential for antiproton--nucleus scattering. In addition, while the full problem is intractable at present, we assess the potential impact of many--nucleon dynamics on scattering observables. We additionally present an analytic computation of the nuclear kinetic density distribution, derived from the nonlocal nuclear densities. While the nuclear problem has become increasingly tractable, the computational barrier is still ever present, with nuclear calculations pushing the frontier of modern supercomputing. Many approaches have been developed to quell the computational demand, e.g. the similarity renormalization group approach. We introduce and discuss another approach, namely the natural orbitals unitary transformation, which has been shown increase the convergence rate of quantum many--body calculations. Lastly, in the past three years there has revitalized interest in reevaluation of particular Standard Model symmetries. Notably, the Cabibbo--Kobayashi--Maskawa quark mixing matrix has been established as a high--precision test of the Standard Model, capable of pointing to novel physics. Recent theoretical advances in corrections needed to evaluate unitarity of the Cabibbo--Kobayashi--Maskawa matrix have indicated a statistical discrepancy with the Standard Model expectation. In light of this development, using the ab initio no--core shell model with continuum, we pursue a high--precision calculation of the isospin symmetry breaking correction, $\delta_C$. This correction is one of two nuclear structure dependent corrections needed to shed light on this discrepancy, and potentially identify physics beyond the Standard Model. / Graduate

Despite decades of theoretical and experimental investigation, the fundamental interactions between nucleons remains poorly understood. While the strong interaction is responsible for binding quarks into nucleons, and nucleons into nuclei, there is no consistent description of these processes. At the low energies where nucleon binding occurs, the interactions are in principle calculable from quantum chromodynamics, but the required non-perturbative calculations are not possible. Instead, different models have been created to describe different phenomena. These models require experimental input to constrain them. As the expected weak interaction effects are not seen in the strangeness-conserving systems as have been seen in other systems, it is believed that the strong interaction interferes with the weak interaction. Therefore by measuring parity-violating observables that occur due to the weak interaction, information can be gained about the strong interaction. The NPDGamma and n3He experiments are two complementary experiments that measured a parity violating observables in a few nucleon system. They ran on the Fundamental Neutron Physics Beamline at the Spallation Neutron Source. The NPDGamma experiment measured the parity violating directional asymmetry in the gamma ray's emission direction after polarized cold neutron capture on a liquid parahydrogen target using an array of 48 CsI detectors. The n3He experiment measured the parity violating directional asymmetry in the proton emission direction after polarized cold neutron capture on a gaseous $^{3}$He target. The capture occurs inside an ionization chamber that measures the proton emission direction. Both experiments have completed data taking with data analysis in an advanced state. These experiments should be able to be used with a number of already existing experimental results to constrain the models. I designed and assembled a pair of $^{3}$He ionization chambers that were used as beam monitors during the experiments. Using the lessons learned from the beam monitors, I then designed and assembled the ionization chamber that is the combined target and detector for the n3He experiment. The monitors and target chamber were examined to determine their charge collection properties and linearity after installation. One of the monitors was calibrated to determine the neutron flux from the output current. / February 2017