Neutron Spin Rotation Measurements by the NSR Collaboration

To constrain weak coupling constants between nucleons and place limits on the existence of possible long-range forces, the Neutron Spin Rotation (NSR) apparatus measures rotations of transversely-polarized neutrons passing through $\sim0.5$~m of target material [1,2]. A previous measurement on the NG6 beamline at the NCNR placed stringent limits on the size of parity-violating rotations of neutrons in liquid helium, $d\phi/dz = \left[ +1.7 \pm 9.1 (stat.)\pm1.4(sys.)\right] \times 10^{-7}$~rad/m [1]. A newly designed apparatus will accept the increased phase-space of the new high-flux NGC beam at NCNR to improve this statistically-limited measurement by about an order of magnitude. An experiment using the same apparatus with a room-temperature target is being proposed at LANSCE to place limits on parity-conserving rotations from possible fifth-force interactions to complement previous studies [3,4]. An overview of the experimental method, plans for upcoming measurements, and the status of upgrades will be presented.\\[4pt] [1] W. M. Snow et al., PRC {\bf 83}, 022501(R) (2011) \newline [2] H. Yan, W. M. Snow, PRL {\bf 110}, 082003 (2013)\newline [3] E. G. Adelberger, T.A. Wagner, PRD {\bf 88}, 031101(R) (2013)\newline [4] F. M. Piegsa, G. Pignol, PRL {\bf 108}, 181801 (2012)