Measurement of the Target-Normal Single-Spin Asymmetry in Deep-Inelastic Scattering from the Reaction ³He↑(e,e\u27)X

We report the first measurement of the target-normal single-spin asymmetry in deep-inelastic scattering from the inclusive reaction 3He↑(e, e\u27)X on a polarized 3He 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 \u3c W \u3c 2.9 GeV, 1.0 \u3c Q2 \u3c 4.0 GeV2 and 0.16 \u3c x \u3c 0.65. Neutron asymmetries were extracted using the effective nucleon polarization and measured proton-to-3He cross-section ratios. The measured neutron asymmetries are negative with an average value of (-1.09 ± 0.38) x 10-2for invariant mass W \u3e 2 GeV, which is nonzero at the 2.89σ 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