Measurement of the neutron decay electron-antineutrino angular correlation by the aCORN experiment

The aCORN experiment measures the neutron-decay electron-antineutrino correlation ($a$ coefficient) using a novel method based on an asymmetry in proton time-of-flight for events where beta electron and recoil are detected delayed coincidence. We report data analysis result from second run at NIST Center Neutron Research, high-flux cold neutron beam new NG-C guide end position: $a=\ensuremath{-}0.10758\ifmmode\pm\else\textpm\fi{}0.00136(\text{stat})\ifmmode\pm\else\textpm\fi{}0.00148(\text{sys})$. This is consistent within uncertainties with first NG-6 beam. Combining two runs, we obtain $a=\ensuremath{-}0.10782\ifmmode\pm\else\textpm\fi{}0.00124(\text{stat})\ifmmode\pm\else\textpm\fi{}0.00133(\text{sys})$, which has overall relative standard uncertainty of 1.7%. corresponding ratio weak coupling constants $\ensuremath{\lambda}={G}_{A}/{G}_{V}$ $\ensuremath{\lambda}=\ensuremath{-}1.2796\ifmmode\pm\else\textpm\fi{}0.0062$.