abstract: This work presents analysis and results for the NPDGamma experiment, measuring the spin-correlated photon directional asymmetry in the $\vec{n}p\rightarrow d\gamma$ radiative capture of polarized, cold neutrons on a parahydrogen target. The parity-violating (PV) component of this asymmetry $A_{\gamma,PV}$ is unambiguously related to the $\Delta I = 1$ component of the hadronic weak interaction due to pion exchange. Measurements in the second phase of NPDGamma were taken at the Oak Ridge National Laboratory (ORNL) Spallation Neutron Source (SNS) from late 2012 to early 2014, and then again in the first half of 2016 for an unprecedented level of statistics in order to obtain a measurement that is precise with respect to theoretical predictions of $A_{\gamma,PV}=O(10^{-8})$. Theoretical and experimental background, description of the experimental apparatus, analysis methods, and results for the high-statistics measurements are given. / Dissertation/Thesis / Doctoral Dissertation Physics 2017

Weak nucleon nucleon couplings are largely unknown because of the involved theoretical and experimental challenges. Theoretically the topic is difficult due to the non-perturbative nature of the strong interaction, which makes calculations of the couplings challenging. Experimentally, the topic is difficult given that 1) the observables are determined by ratios between strong couplings and weak couplings which differ in size by seven orders of magnitude, and 2) theoretically clean and predictable measurements are almost always restricted to simple systems that do not allow for effects that enhance the size of the asymmetry. However parity violation (PV) can be used to separate out the weak part and thus studies of PV in hadronic systems could offer a unique probe of nucleon structure. The n-3He experiment at the Spallation Neutron Source was performed to measure the parity violating asymmetry of the recoil proton momentum kp with respect to the neutron spin in the reaction n + 3He ---> p + T + 764 keV. This asymmetry is sensitive to the isospin-conserving and isospin-changing (∆I = 0, 1, 2) parts of the Hadronic Weak Interaction (HWI), and is expected to be small (~10-7). The goal of this experiment was to determine this PV asymmetry with a statistical sensitivity of 2x10-8. We also measured the parity even nuclear asymmetry proportional to kp · σn x kn for the first time for verification of nuclear theory and for confirmation of the sensitivity of our experiment to the parity violating asymmetry.