aCORN: Measuring the electron-antineutrino correlation in neutron beta decay

The electron-antineutrino correlation ($a$-coefficient) is one of several important experimentally measured parameters of neutron beta decay. Together these parameters are used to determine the charged current weak couplings of free neutrons and protons, measure the CKM matrix element $V_{ud}$, and perform precision tests of physics beyond the Standard Model. The aCORN experiment uses a novel ``wishbone asymmetry'' method to measure the $a$-coefficient that does not require precision proton spectroscopy. aCORN completed two physics runs at the NIST Center for Neutron Research. The first run on the NG-6 beam line obtained the result $a = -0.1090 \pm 0.0030\mbox{(stat)}\pm 0.0028\mbox{(sys)}$, the most precise measurement of the neutron $a$-coefficient to date. The second run on the new NG-C high flux beam line promises a significant improvement in precision. Details of the experiment and data analysis will be presented.