# Undetected Electron Backscattering in PERKEO III

## TL;DR

This paper quantifies the correction needed for undetected electron backscattering in neutron beta decay experiments using PERKEO III, significantly reducing systematic errors in measuring beta asymmetry.

## Contribution

It provides the first detailed determination of undetected backscattering correction for electron detection in PERKEO III, improving measurement accuracy.

## Key findings

- Undetected backscattering correction is 5×10⁻⁴ for electron asymmetry.
- Backscattering correction accounts for 40% of the total systematic uncertainty.
- Improves precision in neutron beta decay measurements.

## Abstract

The beta asymmetry in neutron beta decay is used to determine the ratio of axial-vector coupling to vector coupling most precisely. In electron spectroscopy, backscattering of electrons from detectors can be a major source of systematic error. We present the determination of the correction for undetected backscattering for electron detection with the instrument PERKEO III. For the electron asymmetry, undetected backscattering leads to a fractional correction of $5\times 10^{-4}$, i.e. a change by 40% of the total systematic uncertainty.