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Neutron Spin Rotation Measurements



Jeffrey S. Nico, Shannon Hoogerheide, Hans Pieter Mumm, Murad Sarsour, J Amadio, Eamon Anderson, Libertad Barron-Palos, Bret Crawford, Chris Crawford, D. Esposito, Walter Fox, I Francis, J Fry, Chris Haddock, Adam Holley, Kirill Korsak, J Lieers, S Magers, M. Maldonado-Velazquez, D Mayorov, T Okudaira, C Paudel, S Santra, H.M. Shimizu, William M. Snow, A. Sprow, K. Steen, H E. Swanson, John Vanderwerp, P. A. Yergeau


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, dφ/dz = [+1.7 ± 9.1 (stat.) ± 1.4 (sys.)] × 10−7 rad/m, 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 NIST Center for Neutron Research, the apparatus was upgraded to take advantage of the larger-area and more divergent NG-C beam. Significant improvements are also being made to the cryogenic design. Details of these improvements and readiness of the upgraded apparatus are presented. We also comment on how recent theoretical work combining effective field theory techniques with the 1/Nc expansion of QCD along with previous NN weak measurements can be used to make a prediction for dφ/dz in 4He. An experiment using the same apparatus with a room-temperature target was carried out at LANSCE to place limits on parity-conserving rotations from possible fifth-force interactions to complement previous studies. We sought this interaction using a slow neutron polarimeter that passed transversely polarized slow neutrons by unpolarized slabs of material arranged so that this interaction would tilt the plane of polarization and develop a component along the neutron momentum. The results of this measurement and its impact on the neutron-matter coupling g2A from such an interaction are presented.
Conference Dates
May 24-26, 2018
Conference Location
Grenoble, FR
Conference Title
Workshop on Particle Physics at Neutron Sources


neutron polarization, neutron spin rotation, hadronic parity violation, weak interaction


Nico, J. , Hoogerheide, S. , Mumm, H. , Sarsour, M. , Amadio, J. , Anderson, E. , Barron-Palos, L. , Crawford, B. , Crawford, C. , Esposito, D. , Fox, W. , Francis, I. , Fry, J. , Haddock, C. , Holley, A. , Korsak, K. , Lieers, J. , Magers, S. , Maldonado-Velazquez, M. , Mayorov, D. , Okudaira, T. , Paudel, C. , Santra, S. , Shimizu, H. , Snow, W. , Sprow, A. , Steen, K. , Swanson, H. , Vanderwerp, J. and Yergeau, P. (2021), Neutron Spin Rotation Measurements, Workshop on Particle Physics at Neutron Sources, Grenoble, FR, [online],, (Accessed April 17, 2024)
Created April 15, 2021, Updated March 30, 2022