We report the first measurement of the target-normal single-spin asymmetry in deep-inelastic scattering from the inclusive reaction 3He↑(e,e′)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<W<2.9 GeV, 1.0<Q2<4.0 GeV2 and 0.16<x<6.5. 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)×10−2 for invariant mass W>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.
Digital Object Identifier (DOI)
This work was supported in part by the U.S. National Science Foundation, the UK Science and Technology Facilities Council, the U.S. Department of Energy and by DOE Contract No. DE-AC05-06OR23177, under which Jefferson Science Associates, LLC, operates the Thomas Jefferson National Accelerator Facility.
Allada, K.; Dutta, C.; Kolarkar, A.; Korsch, Wolfgang; Katich, J.; Qian, X.; Zhao, Y. X.; Aniol, K.; Annand, J. R. M.; Averett, T.; Benmokhtar, F.; Bertozzi, W.; Bradshaw, P. C.; and Bosted, P., "Measurement of the Target-Normal Single-Spin Asymmetry in Deep-Inelastic Scattering from the Reaction 3He↑(e,e′)X" (2014). Physics and Astronomy Faculty Publications. 322.