Recoil-Order and Radiative Corrections to the aCORN Experiment

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 $\overline{a}=-0.10779\pm 0.00125(\mathrm{stat})\pm 0.00133(\mathrm{sys})$, averaged over the full Fermi neutron beta spectrum. The corresponding corrected result for the ratio of weak coupling constants $\hat{I}»=G_A/G_V$ is $\hat{I}»=-1.2712\pm 0.0061$. This improves agreement with previous $a$-coefficient experiments, in particular the 2020 aSPECT result