A Precision Measurement of the Weak Charge of Proton at Low Q^2: Kinematics and Tracking

Abstract

The Standard Model of particle physics represents our present best understanding of the elementary particles and three of the four fundamental forces. One of the most important and challenging tasks of modern particle physics is to test, and perhaps, to find the evidence for new physics not contained in the Standard Model. One such test, the $Q_{weak}$ experiment, was conducted at JLab in Newport News, VA, from 2010 to 2012. The goal of the experiment is to measure the value of the weak charge of proton, $Q_{weak}$ to a 4\% precision, which, if it confirms the Standard Model prediction, will provide tighter constraints on new physics; or, if it is in disagreement with that prediction, will provide clear evidence for new physics. In this experiment, an 85\% polarized electron beam with 150 $\mu A$ current is used on a 35cm thick hydrogen target to make elastic electron-proton scattering happen at a four-momentum transfer $Q^2=0.03GeV/c^2$. to determine the weak charge, we must also precisely determine the kinematics of the scattering process, namely, the $Q^2$. In order to reach this goal, the hardware, a particle tracking system and special analysis software, the Qweak Tracking Reconstruction software, are both needed. In this dissertation, a full description of the tracking software and the prelimary analysis of the $Q^2$ and the first subset of production data will be given. The proton\u27s weak charge $Q^P_{Weak}$ was measured to be $0.064\pm0.012$, which is consistent with the prediction of the Standard Model