Recoil-Order and Radiative Corrections to the aCORN Experiment

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 a = -0.10779 ± 0.00125 ( stat) ± 0.00133 ( sys), averaged over the full Fermi neutron beta spectrum. The corresponding corrected result for the ratio of weak coupling constants λ = G_A/G_V is λ = -1.2712 ± 0.0061. This improves agreement with previous a-coefficient experiments, in particular the 2020 aSPECT result