Observation of Target Electron Momentum Effects in Single-Arm M\o ller Polarimetry

TL;DR

This paper investigates how target electron momentum influences Møller polarimetry measurements, demonstrating that accounting for this effect is crucial for accurate polarization determination and matching experimental observations.

Contribution

It provides experimental evidence of electron momentum effects in Møller polarimetry and shows their impact on polarization measurements and simulation accuracy.

Findings

Target electron momentum affects measured polarization by -14%.

Including the effect aligns measurements with Compton polarimeter results.

The effect is essential for accurate simulation of scattering peaks.

Abstract

In 1992, L.G. Levchuk noted that the asymmetries measured in M\o ller scattering polarimeters could be significantly affected by the intrinsic momenta of the target electrons. This effect is largest in devices with very small acceptance or very high resolution in laboratory scattering angle. We use a high resolution polarimeter in the linac of the polarized SLAC Linear Collider to study this effect. We observe that the inclusion of the effect alters the measured beam polarization by -14% of itself and produces a result that is consistent with measurements from a Compton polarimeter. Additionally, the inclusion of the effect is necessary to correctly simulate the observed shape of the two-body elastic scattering peak.