Date of Award

August 2020

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Physics

Advisor(s)

Paul Souder

Keywords

Beam Correction, Parity Asymmetry, Parity Violation, Scattering, Standard Model, Weak Charge

Subject Categories

Physical Sciences and Mathematics

Abstract

The weak charge of the proton is determined via Qweak experiment at Thomas Jefferson Laboratory in Newport News, VA. A longitudinally polarized electron beam was scattered by a liquid hydrogen target. The spin direction of the electron beam was switched between left and right helicity states. The cross section under both of the electron states were measured to form the parity-violating asymmetry. An asymmetry of -226.5±7.3(stat)±5.8(syst) was measured, corresponding to a weak charge of 0.0719±0.0045 for the proton, which agrees with the value of 0.0708±0.0003 from the Standard Model.

During the spin reversion of the electrons, other unwanted changes of the electron beam can be introduced as well to cause false cross section changes, also known as the "false" asymmetry. Successful evaluation and removal of these false asymmetries are crucial to the accuracy of the final measured results. In this thesis, the methods of beam correction, including regression, are discussed in detail about how the false asymmetry removal is done and how the results of the experiment can be more robust under such corrections. Other asymmetry corrections terms are discussed as well, including beam current asymmetry correction.

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Open Access

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