Status of an Experiment to Measure the Parity-odd NeutronSpin Rotation in ⁴He

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 ⁴He just outside the previous measurement of dφ/dz = [+2.1 ± 8.3(stat.) ± 2.9(sys.)] × 10⁻⁷ rad/m [4]. This prediction will be updated in light of the recent measurement in the n-3He system [5]. Upgrades to the NSR apparatus enable an experimental sensitivity < [±1.0(stat.) ± 1.0(sys.)] × 10⁻⁷ rad/m [6] on the NG-C beamline at NIST. The current status of the NSR apparatus will be discussed.

[1] S. Gardner, W. C. Haxton, and B. R. Holstein, Ann. Rev. Nucl. Part. Sci. 67, 69, 024001,(2017).

[2] R. Lazauskas and Y.-H Song, Phys. Rev. C 99, 054002 (2019).

[3] D. Blythet al.(NPDGamma Collaboration), Phys. Rev. Lett. 121, 242002 (2018).

[4] H. E. Swanson,et al., Phys. Rev. C 100, 015204 (2019).

[5] M. T. Gericke,et al., Phys. Rev. Lett. 125, 131803, (2020).

[6] W. M. Snow,et al., Rev. Sci. Inst. 94, 055101, (2015).