Parity-Violating Neutron Spin Rotation in n-$^4$He

The neutron spin rotation (NSR) collaboration used parity-violating spin rotation of transversely polarized neutrons transmitted through a 0.5 m liquid helium target to constrain weak coupling constants between nucleons. While consistent with theoretical expectation, the upper limit set by this measurement on the rotation angle, d$\phi$/dz = [+1.7 $\pm$ 9.1(stat.) $\pm$1.4(sys.)]$\times 10^{-7}$ rad/m ~\footnote{W. M. Snow et al., PRC \textbf{83}, 022501(R) (2011).}, is limited by statistical uncertainties. The NSR collaboration is preparing a new measurement to improve this statistically-limited result by about an order of magnitude. In addition to using the new high-flux NG-C beam at the National Institute of Standards and Technology (NIST) Center for Neutron Research, the apparatus is being upgraded to take advantage of the larger-area and more divergent NG-C beam. In addition, significant improvements have been made to the cryogenic design and the $^3$He ion chamber. Details of these improvements and readiness of the upgraded apparatus will be discussed and the current theoretical and experimental status of d$\phi$/dz in n-$^{4}$He will be reviewed.