Abstract
We report the first measurement of the target-normal single-spin asymmetry in deep-inelastic scattering from the inclusive reaction on a polarized 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 , and . Neutron asymmetries were extracted using the effective nucleon polarization and measured proton-to- cross-section ratios. The measured neutron asymmetries are negative with an average value of for invariant mass , which is nonzero at the 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.
- Received 7 November 2013
DOI:https://doi.org/10.1103/PhysRevLett.113.022502
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