High-precision Compton Polarimetry for the MOLLER Experiment*

The MOLLER experiment will make an ultra-high precision measurement of parity violation in electron-electron scattering as a sensitive search for new fundamental physics. Compton polarimetry provides a powerful non-invasive method to determine the polarization of high-energy electron beams with high precision. We present the design and development of a Compton polarimeter which will achieve a polarization measurement with 0.4% precision for the 11 GeV electron beam used for MOLLER. The design utilized a Fabry-Perot optical cavity storing 532~nm laser light, intersecting the electron beam. This system support control of laser polarization at the level of 0.1% and employs a helicity-reversed electron beam to determine the scattering asymmetry. The polarimeter employs both electron and photon detectors with a data acquisition system optimized for the control of systematic uncertainty in the extraction of the electron beam polarization from the scattering asymmetry. By combining precise optical control with robust detection, this system supports highly accurate of Compton-based polarization measurements and provides an essential diagnostic for precision parity-violation experiment like MOLLER.