Physical Review Letters
We report the first measurement of the target-normal single-spin asymmetry in deep-inelastic scattering from the inclusive reaction He-3(up arrow)(e, e')X on a polarized He-3 gas target. Assuming time-reversal invariance, this asymmetry is strictly zero in the Born approximation but can be nonzero if two-photon-exchange contributions are included. The experiment, conducted at Jefferson Lab using a 5.89 GeV electron beam, covers a range of 1.7 < W < 2.9 GeV, 1.0 < Q(2) < 4.0 GeV2 and 0.16 < x < 0.65. Neutron asymmetries were extracted using the effective nucleon polarization and measured proton-to-He-3 cross-section ratios. The measured neutron asymmetries are negative with an average value of (-1.09 +/- 0.38) x 10(-2) for invariant mass W > 2 GeV, which is nonzero at the 2.89 sigma level. Our measured asymmetry agrees both in sign and magnitude with a two-photon-exchange model prediction that uses input from the Sivers transverse momentum distribution obtained from semi-inclusive deep-inelastic scattering.
Katich, J., Qian, X., Zhao, Y. X., Allada, K., Aniol, K., Annand, J. R. M., ... & Bosted, P. (2014). Measurement of the Target-Normal Single-Spin Asymmetry in Deep-Inelastic Scattering from the Reaction He 3↑(e, e′) X. Physical review letters, 113(2), 022502.