Doctor of Philosophy (Ph.D.)
Gregory R Smith
The Qweak collaboration has made the first measurements of the elastic parity-violating and beam-normal single-spin asymmetries from the 27Al 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, Qp W, 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 27Al 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 27Al asymmetry, and the determination of the elastic beam-normal single-spin 27Al asymmetry. The parity-violating result was also used to make a semi model-independent determination 27Al 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 208Pb, as 27Al is the next highest atomic mass nucleus to have this observable measured.
The elastic parity-violating 27Al asymmetry was found to be $1.927 ± 0.173 ppm at ⟨ Q2 ⟩ = 0.0236 ± 0.0001 GeV2. This measured parity-violating asymmetry implies a 27Al neutron distribution radius of $3.024 ± 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 ± 0.104 fm. This skin value is consistent with zero, within its uncertainty, and it confirms the naive expectation for a light nucleus like 27Al.
The beam-normal single-spin 27Al asymmetry was found to be $-16.322 ± 2.679 ppm at ⟨ Q ⟩ = 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.
© The Author
Bartlett, Kurtis David, "First Measurements of the Parity-Violating and Beam-Normal Single-Spin Asymmetries in Elastic Electron-Aluminum Scattering" (2018). Dissertations, Theses, and Masters Projects. Paper 1550153799.