Status of an Experiment to Measure the Parity-odd Neutron Spin Rotation in$\hspace{2mm}^4$He

The NN weak interaction is sensitive to quark-quark correlations in the nucleon and provides the means to test the Standard Model in the low energy strongly interacting limit. Recent theoretical work [1,2] along with the measurement of the weak pion exchange component of the NN weak interaction [3] implies a large parity-odd neutron spin rotation in $^{4}$He just outside the previous measurement of $d\phi/dz = [+2.1 \pm 8.3(stat.) \pm 2.9(sys.)] \times 10^{-7}$ rad/m [4]. Upgrades to the NSR apparatus enable an experimental sensitivity $< [\pm 1.0(stat.) \pm 1.0(sys.)] \times 10^{-7}$ rad/m [5] on the NG-C beamline at NIST. The status of the NSR apparatus as well as implications of the recent measurement in the n-3He system [6] will be discussed. \\ \\{[1]} S. Gardner, W. C. Haxton, and B. R. Holstein, Ann. Rev. Nucl. Part. Sci. \textbf{67}, 69, 024001, (2017). \\{[2]} R. Lazauskas and Y.-H Song, Phys. Rev. C {\bf 99}, 054002 (2019). \\{[3]} D. Blyth {\it et al.} (NPDGamma Collaboration), Phys. Rev. Lett. {\bf 121}, 242002 (2018). \\{[4]} H. E. Swanson, {\it et al.}, Phys. Rev. C {\bf 100}, 015204 (2019). \\{[5]} W. M. Snow, {\it et al.}, Rev. Sci. Inst. \textbf{94}, 055101, (2015). \\{[6]} M. T. Gericke, {\it et al.}, Accepted to arXiv, (2020).