An Improved Measurement of the Neutron Decay Beta-Neutrino Correlation with the aCORN Experiment

The decay of the free neutron into a proton, electron, and antineutrino is the simplest example of nuclear beta decay. The electron-antineutrino correlation (a-coefficient) is one of several important experimental parameters of neutron decay. Together these parameters can be used to determine the charged weak couplings of neutrons and protons, measure the CKM matrix element V_ud, and conduct precision low energy tests of physics beyond the Standard Model. The aCORN experiment uses a novel “wishbone asymmetry” method that does not require detailed proton spectroscopy to measure the neutron a-coefficient The first aCORN run in 2013–2014 produced the most precise measurement to date. The second run in 2015–2016 on the new high-flux beamline NG-C at the NIST Center for Neutron Research collected a ten-times larger data set. Details of the experiment and results from the NG-C run will be presented.