aCORN: A Precision Measurement of the Neutron Decay $a$-coefficient

The aCORN experiment will make a precision ($<1$\%) measurement of the electron-antineutrino angular correlation ($a$- coefficient) in neutron beta decay. It uses a novel collimation geometry in which the $a$-coefficient is proportional to an asymmetry in beta-proton coincidence count rates, so that precision spectroscopy of the particles is not necessary. The apparatus is now being constructed; it will be integrated and tested at the new LENS facility at Indiana University in 2007 and then moved to the NIST Center for Neutron Research for a precision physics measurement in 2008. The current status of design and construction will be presented. Work supported by NSF grants PHY-0420851, PHY-0420361, PHY-0420716, PHY-0420563, and NIST (U.S. Dept. of Commerce).