A novel comparison of M{\o}ller and Compton electron-beam polarimeters

TL;DR

This study compares M{46}ller and Compton electron-beam polarimeters at Jefferson Lab, confirming their measurements agree within 1% across different beam currents, supporting their use in high-precision experiments.

Contribution

It provides the first direct comparison of M{46}ller and Compton polarimeters at low and high beam currents, validating their consistency for precision polarization measurements.

Findings

Measurements agree within 1% across beam currents

Electron polarization is independent of beam current

Sets benchmark for future high-precision polarimetry

Abstract

We have performed a novel comparison between electron-beam polarimeters based on M{\o}ller and Compton scattering. A sequence of electron-beam polarization measurements were performed at low beam currents ($<$ 5 $\mu$A) during the $Q_{\rm weak}$ experiment in Hall C at Jefferson Lab. These low current measurements were bracketed by the regular high current (180 $\mu$A) operation of the Compton polarimeter. All measurements were found to be consistent within experimental uncertainties of 1% or less, demonstrating that electron polarization does not depend significantly on the beam current. This result lends confidence to the common practice of applying M{\o}ller measurements made at low beam currents to physics experiments performed at higher beam currents. The agreement between two polarimetry techniques based on independent physical processes sets an important benchmark for future precision asymmetry measurements that require sub-1% precision in polarimetry.