Year of Publication

2015

Degree Name

Doctor of Philosophy (PhD)

Document Type

Doctoral Dissertation

College

Arts and Sciences

Department

Physics and Astronomy

First Advisor

Dr. Christopher B. Crawford

Abstract

The NPDGamma Experiment is used to study the n + p to d + g reaction for the purpose of examining the hadronic weak interaction. The nucleon-nucleon interaction is overwhelmingly mediated by the strong force, however, the weak part can be extracted by a study of its parity violating manifestations. When neutrons are incident on protons, deuterons and 2.2 MeV gamma rays are produced. If the incoming neutrons are polarized, the parity violating weak interaction gives rise to a measured spatial asymmetry, Ag, in the outgoing gamma rays, as sn · kg is parity odd.

At low energies, the weak nucleon-nucleon interaction can be modeled as meson exchange and characterized with six parameters. NPDGamma is sensitive to one of these parameters, hp. Previous measurements that extrapolate hp from more complicated interactions disagree, and disagree with the theoretical reasonable range. Additionally, a previous iteration of the NPDGamma Experiment performed at Los Alamos National Lab was statistics limited in its measurement of Ag. For this reason, a new measurement was performed at the high neutron flux Spallation Neutron Source at Oak Ridge National Lab.

In the experiment, a high flux of cold neutrons was polarized to ~ 95% by a supermirror polarizer, the spins flipped in a defined sequence by a radio-frequency spin rotator, and then the neutrons captured on a 16 L liquid para-hydrogen target, which emits gamma-rays asymmetrically upon capture. The gamma-rays are detected in a 3pi array of 48 CsI crystal detectors. This thesis discusses the NPDGamma Experiment in detail, and includes an analysis of subset of the NPDGamma data that has unique timing and data acquisition properties that preclude it being analyzed with the combined data set. Ag was extracted with a result of (6.254 ± 37.694) × 10-9

Included in

Nuclear Commons

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