Measurement of the Neutron Spin Polarization in Deuteron Photodisintegration Near Threshold

As the only known two-nucleon bound state, the deuteron offers a unique opportunity to study the interactions between nucleons. Nuclear theory has developed a number of models and theories to describe the strong nuclear force in the low energy regime of quantum chromodynamics (QCD). Contemporary theories have been fit to unpolarized nucleon-nucleon scattering cross sections rather successfully, lending credence to multiple approaches to modeling the nuclear force. Investigations of spin polarization degrees of freedom in nuclear reactions provide additional rigorous tests of nuclear theory. The spin polarization induced on the neutron in deuteron photodisintegration has been previously measured for insight into nucleon-nucleon interactions. These past measurements demonstrated notable discrepancies with theoretical predictions, prompting questions about the implications for either the experimental methodology or the underlying theory.

This dissertation details a measurement of the spin polarization of the neutron from deuteron photodisintegration performed at the High Intensity Gamma-Ray Source (HIGS) using a 16 MeV photon beam with circular polarization. It served as one of a series of measurements of this observable near the energy threshold for photodisintegration to investigate the long-standing discrepancies between previous experimental measurements and theoretical calculations. Innovations in accelerator technology and spin polarization techniques have offered new capabilities in obtaining a precise result. The experimental setup used a heavy water (2H2O) target surrounded by high pressure gas 4He-Xe polarization analyzers at laboratory reaction angles of interest. Liquid organic scintillator detectors on each side of an analyzer acted as neutron counting detectors, to measure the left-right scattering asymmetry of polarized neutrons from the analyzers. The neutron polarization was extracted from the scattering asymmetry for comparisons to theoretical predictions and previous measurements.