Testing the Standard Model with Parity-Violating Electron Scattering

A central goal of contemporary fundamental physics is to find evidence for new physics, beyond the scope of the Standard Model of particle physics, and to characterize its features once such evidence is found. One avenue to search for new physics is the "Precision frontier" where precise measurements are made of quantities that are precisely predicted by the Standard Model - a deviation from this prediction would signal new physics. This project supports one such measurement, the MOLLER experiment, which will determine the electron-electron weak interaction to unprecedented precision, using the electron accelerator at the Thomas Jefferson National Accelerator Facility. The team will construct and commission several components of the particle detection system and will develop the particle-tracking software to be used in the data analysis. Graduate students and a postdoctoral researcher will actively participate and thereby develop skills in precision nuclear physics experimentation and in the analysis of large and complex data sets. The MOLLER experiment will use parity-violating electron-electron scattering to extract 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 expected 35 ppb parity-violating asymmetry in the scattering cross section will be determined to a precision of 0.5 ppb, five times smaller than the only previous measurement. The William & Mary group will provide the detector system used to characterize one of the most important background processes, electro- and photo-production of pions, and will lead the effort to create and commission the particle-reconstruction software used in the calibration of the spectrometer acceptance and to correct for various backgrounds. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.