Recoil-Order and Radiative Corrections to the aCORN Experiment

TL;DR

This paper refines the measurement of the neutron decay a-coefficient by including first-order radiative and recoil corrections, leading to more accurate results that align better with previous experiments.

Contribution

It introduces first-order radiative and recoil corrections to the aCORN experiment's neutron decay measurements, improving the accuracy and consistency of the results.

Findings

Corrected a-coefficient: -0.10779 ± 0.00125 (stat) ± 0.00133 (sys)

Corrected lambda: -1.2712 ± 0.0061

Enhanced agreement with previous experiments, especially 2020 aSPECT

Abstract

The aCORN experiment measures the electron-antineutrino $a$-coefficient in free neutron decay. We update the previous aCORN results to include radiative and recoil corrections to first order, and discuss a key issue in the comparison of results from different $a$-coefficient experimental methods when these effects are considered. The corrected combined result is $\overline{a} = -0.10779 \pm 0.00125\, ({\rm stat}) \pm 0.00133\, ({\rm sys})$, averaged over the full Fermi neutron beta spectrum. The corresponding corrected result for the ratio of weak coupling constants $\lambda = G_A/G_V$ is $\lambda = -1.2712 \pm 0.0061$. This improves agreement with previous $a$-coefficient experiments, in particular the 2020 aSPECT result