Measurement of the Electron-Antineutrino Angular Correlation in Neutron <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>β</mml:mi></mml:math> Decay

Abstract

We report the first result for the electron-antineutrino angular correlation ($a$ coefficient) in free neutron $\ensuremath{\beta}$ decay from the aCORN experiment. aCORN uses a novel method in which the $a$ coefficient is proportional to an asymmetry in proton time of flight for events where the $\ensuremath{\beta}$ electron and recoil proton are detected in delayed coincidence. Data are presented from a 15 month run at the NIST Center for Neutron Research. We obtained $a=\ensuremath{-}0.1090\ifmmode\pm\else\textpm\fi{}0.0030(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.0028(\mathrm{sys})$, the most precise measurement of the neutron $a$ coefficient reported to date.