Measurement of the Target-Normal Single-Spin Asymmetry in Deep-Inelastic Scattering from the Reaction \(^{3}\mathrm{He}^{\uparrow}(e,e')X\)

Abstract

We report the first measurement of the target-normal single-spin asymmetry in deep-inelastic scattering from the inclusive reaction \(^3\)He\(^{\uparrow}\left(e,e' \right)X\) on a polarized \(^3\)He gas target. Assuming time-reversal invariance, this asymmetry is strictly zero in the Born approximation but can be non-zero 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, \(1.0<Q^2<4.0\) GeV\(^2\) and \(0.16<x<0.65\). Neutron asymmetries were extracted using the effective nucleon polarization and measured proton-to-\(^3\)He cross section ratios. The measured neutron asymmetries are negative with an average value of \((-1.09 \pm 0.38) \times10^{-2}\) for invariant mass \(W>2\) GeV, which is non-zero 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.