Probing the Standard Model and Nuclear Structure with Parity-Violating Electron Scattering

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This project supports research that seeks to answer a fundamental question about matter. What is the nature of any new physics not described by the Standard Model - our current understanding of how particles and forces interact? This question will be addressed by precision measurements of the weak charges of the proton and electron at two large collaborative experiments at the Thomas Jefferson National Accelerator Facility (Jefferson Lab) in Newport News, Virginia. The proton and electron's weak charges are the weak force analogs of the common electric charges of these particles. The weak charges are precisely predicted in the Standard Model. Any deviation of measurements from these predictions could be evidence of yet undiscovered massive particles that represent new physics beyond our current understanding. The program will support graduate and undergraduate students and a postdoctoral fellow, who will form an essential part of this project. The anticipated activities cover a range of hardware and software tasks that will provide excellent training for these individuals. This training in fundamental research provides a strong basis for careers both in basic research and in more applied research and industry. The funds provided by this project will support activities on three parity-violating electron scattering experiments at Thomas Jefferson National Accelerator Facility (TJNAF). The Qweak experiment will measure the proton's neutral weak charge via parity-violating electron scattering at very low momentum transfer. The proton's weak charge has a well-defined prediction in the Standard Model; a precise measurement of it is sensitive to many popular scenarios for extending the Standard Model. During the period of this program, the group will primarily be contributing to a complete analysis of the weak charge result as well as finalizing analyses to extract physics results from the Qweak data for two other topics - a probe of hadronic parity violation in the N to Delta transition and a measurement of the transverse asymmetry in Moller scattering. The MOLLER experiment is an approved TJNAF experiment intended for the upgraded 12 GeV TJNAF. It will measure the electron's neutral weak charge by making a precision measurement of the parity-violating asymmetry in the elastic scattering of polarized electrons on unpolarized electrons at a very low momentum transfer. This will result in a determination of the weak mixing angle at low energy with a precision comparable to the best determinations from high-energy colliders. It should have excellent sensitivity to many beyond the Standard Model scenarios. During the period of this project, the group will make important contributions to this experiment by working on beam charge and position monitor upgrades, luminosity monitor and background detector development and construction, scanner detector development, and simulation design studies. Neutron radii in neutron-rich nuclear provide an important test of nuclear structure with applications to neutron star structure and heavy ion collisions. The PREX-II and CREX experiments are anticipated to run in this period and determine the neutron radii in lead-208 and calcium-48. The group will provide large angle scattering monitors and a setup for linearity testing and will contribute to the analysis of beam monitoring and modulation data and data-taking shift support.