Precision M\o ller Polarimetry for PREX and CREX

TL;DR

This paper details the development and operation of a Møller polarimeter achieving sub-1% precision in measuring electron beam polarization for PREX-2 and CREX experiments, crucial for accurate parity violation measurements.

Contribution

It introduces a highly precise Møller polarimeter with systematic uncertainty below 1%, surpassing previous standards and demonstrating its application in key nuclear physics experiments.

Findings

Achieved polarization measurement precision of 0.89% for PREX-2.

Achieved polarization measurement precision of 0.85% for CREX.

Highlighted the importance of accurate atomic wave functions for corrections.

Abstract

The PREX-2 and CREX experiments in Hall A at Jefferson Lab are precision measurements of parity violating elastic electron scattering from complex nuclei. One requirement was that the incident electron beam polarization, typically $\approx$90\%, be known with 1\% precision. We commissioned and operated a M{\o}ller polarimeter on the beam line that exceeds this requirement, achieving a precision of 0.89\% for PREX-2, and 0.85\% for CREX. The uncertainty is purely systematic, accumulated from several different sources, but dominated by our knowledge of the target polarization. Our analysis also demonstrates the need for accurate atomic wave functions in order to correct for the Levchuk Effect. We describe the details of the polarimeter operation and analysis, as well as (for CREX) a comparison to results from a different polarimeter based on Compton scattering.