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. The corrected combined result is $\langle a \rangle = -0.10859 \pm .00125\, ({\rm stat}) \pm 0.00133\, ({\rm sys})$, an increase in magnitude of 0.7 % compared to the overall relative standard uncertainty of 1.7 %, which is unchanged. The corresponding corrected result for the ratio of weak coupling constants $\lambda = G_A/G_V$ is $\lambda = -1.2737 \pm 0.0061$. This improves agreement with previous $a$-coefficient experiments, in particular the 2020 aSPECT result