## Dissertations, Theses, and Masters Projects

#### ORCID ID

0000-0001-6501-4153

2018

Dissertation

#### Degree Name

Doctor of Philosophy (Ph.D.)

Physics

Wouter Deconinck

David Armstrong

Joshua Erlich

Justin Stevens

Gregory R Smith

#### Abstract

The Qweak collaboration has made the first measurements of the elastic parity-violating and beam-normal single-spin asymmetries from the $^{27}$Al nucleus. Both are the result of ancillary measurements conducted during the Qweak experiment at Jefferson Lab. The goal of the experimental was to determine the proton's weak charge, $Q_{W}^{p}$, via a measurement of the elastic parity-violating electron-proton scattering asymmetry. During the experiment, ancillary measurements were made with different beam configurations on a separate aluminum alloy target, in an effort to directly measure the aluminum background coming from the experiment's liquid hydrogen target cell. This dissertation discusses three primary results: the parity-violating $^{27}$Al asymmetry analysis used to correct for the aluminum target background in the final Qweak analysis, its extended analysis leading to the extraction of the pure elastic parity-violating {\aluminum} asymmetry, and the determination of the elastic beam-normal single-spin $^{27}$Al asymmetry. The parity-violating result was also used to make a semi model-independent determination of $^{27}$Al neutron distribution radius, an important test for models used to describe neutron-rich matter. The beam-normal single-spin asymmetry stands to possibly shed light on an observed disagreement between theory and a previous measurement performed on $^{208}$Pb, as $^{27}$Al is the next highest atomic mass nucleus to have this observable measured. The elastic parity-violating $^{27}$Al asymmetry was found to be $1.927 \pm 0.173$ ppm at $\langle Q^{2} \rangle = 0.0236 \pm 0.0001$ GeV$^{2}$. This measured parity-violating asymmetry implies a $^{27}$Al neutron distribution radius of $3.024 \pm 0.104$ fm. Calculating the difference between this radius and the $^{27}$Al proton distribution radius yields the neutron skin, which was found to be $0.092 \pm 0.104$ fm. This skin value is consistent with zero, within its uncertainty, and it confirms the naive expectation for a light nucleus like $^{27}$Al. The beam-normal single-spin $^{27}$Al asymmetry was found to be $-16.322 \pm 2.679$ ppm at $\langle Q \rangle = 0.154$ GeV. This value agrees with the previous observed trend of beam-normal single-spin asymmetries measured from light nuclei, which motivates the need for future measurements of higher atomic mass nuclei.

#### DOI

http://dx.doi.org/10.21220/s2-h63m-ze10