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[PAST EVENT] Valerie Marie Gray: Physics Dissertation Defense
Abstract: The Qweak experiment has testing the Standard Model through making a precise measurement of the weak charge of the proton (Q_W^p). This was done through measuring the parity-violating asymmetry for a polarized electron scattering off of an unpolarized proton. The parity-violating asymmetry measured is directly proportional to the four-momentum transfer (Q2) from the electron to the proton. The extraction of Q_W^p from the measured asymmetry requires a precise Q2 determination. The Qweak experiment had a Q2 = 24.8 ? 0.1 m(GeV2) which achieved the goal of an uncertainty of ? 0.5%. From the measured asymmetry and Q2, Q_W^p was determined to be 0.0719 ? 0.0045, which is in good agreement with the Standard Model prediction. This puts a 7.5 TeV lower limit on new possible ?new physics?. This dissertation describes the analysis of Q2 for the Qweak experiment.
Future parity-violating electron scattering experiments similar to the Qweak experiment, will measure asymmetries to high precision in order to test the Standard Model. These measurements will require the beam polarization to be measured to sub-percent precision. Presently the electron beam polarization is measured through M?ller scattering off of a ferromagnetic foil or through using Compton scattering, both of which can have issues reaching this precision. A novel Atomic Hydrogen M?ller Polarimeter has been proposed as a non-invasive way to measure the polarization of an electron beam via M?ller scattering off of polarized monatomic hydrogen gas. This dissertation describes the development and initial analysis of a Monte Carlo simulation of an Atomic Hydrogen M?ller Polarimeter.
Bio: Valerie Marie Gray is from Baileys Harbor, Wisconsin, from 2007-2011 she attended St. Norbert College in De Pere, Wisconsin, where she graduated with a B.S. in physics and mathematics. She entered William & Mary in 2011 and started working Dr. David Armstrong on the Qweak Experiment and the Atomic Hydrogen M?ller Polarimeter.