Precision Studies of the Standard Model using Parity-Violating Electron Scattering

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In the quest to understand the fundamental structure of matter, most physicists have taken a reductionist approach by breaking down matter into its elementary constituents: electrons, quarks, gluons, etc. In addition to these known elementary particles that constitute the Standard Model of particle physics (our current best theory of the fundamental particles of matter and their interactions), there may exist more as-of-yet undiscovered elementary particles.This project supports efforts to precisely measure so-called electroweak properties of the proton and of the electron in two large experiments at the Thomas Jefferson National Accelerator Facility (Jefferson Lab). Discrepancies between these measurements and the predictions of the Standard Model will point to new physical processes that are not yet included in the Standard Model. In case of agreement certain extensions to the Standard Model will be ruled out.Precision electroweak measurements present a unique approach to test the Standard Model of particle physics at low-energy electron accelerators. Jefferson Lab is currently the world's leading laboratory for these parity-violating electron scattering experiments, and is uniquely suited to complete the ambitious Qweak and MOLLER experiments. The results of both experiments, by themselves but especially in combination with the results from the Large Hadron Collider at CERN, will allow us to constrain models of physics beyond the Standard Model.The Qweak experiment started in May 2010 and collected data until May 2012. The experiment has performed the first determination of the weak charge of the proton with only 5% of the available data, and is aiming to make a precision measurement sensitive to physics beyond the Standard Model with the full data set. The investigators will continue their central role in the track reconstruction, data analysis, and simulation efforts crucial to the successful completion of the experiment. The MOLLER experiment is expected to run as early as 2017, and will measure the electroweak mixing angle to a precision comparable to the best available high-energy measurements through a measurement of the weak charge of the electron. The investigators will take a leading role in the development of the track reconstruction detectors for the MOLLER experiment, and the development of a novel type of electron beam polarimeter based on Moller scattering in polarized atomic hydrogen gas. This new polarimeter will allow the measurement of the electron polarization to the required precision of 0.4% using a technique that will be applicable at other electron accelerators as well.The investigators are working to increase economic and racial diversity in physics through specific recruiting efforts for the William & Mary REU program. The investigators are committed to increasing interaction between the physics department and the broader community through the organization of "PhysicsFest," a yearly physics department open house, and through "Saturday Morning Physics," a regular public outreach lecture series aimed at local middle and high school students.