Precision Standard Model Tests With Parity-Violating Electron Scattering

Virginia Polytechnic Institute And State University, Blacksburg VA

Investigators

Abstract

This grant 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. The proton and electron's weak charges are the weak force analogs of the ordinary 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 as yet undiscovered massive particles that represent new physics beyond our existing understanding. The grant will support graduate and undergraduate students who will form an essential part of this project. The anticipated activities cover a range of hardware and software projects that will provide excellent training for these students. 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 grant will support activities on two 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 grant, we will perform data analysis leading to the final determination of the proton's weak charge from the Qweak experiment. We will also perform analysis 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 would have excellent sensitivity to many beyond the Standard Model scenarios. During the period of this grant, our group will contribute to the development of this experiment by working on beam charge and position monitor upgrades, luminosity monitor and background detector development and construction, and simulation design studies.