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.

Document Type


Publication Date


Notes/Citation Information

Published in Physical Review Letters, v. 113, no. 2, article 022502, p. 1-6.

©2014 American Physical Society

The copyright holder has granted permission for posting the article here.

Due to the large number of authors involved, only the first 10 and the ones affiliated with the University of Kentucky are listed in the author section above. For the complete list of authors, please download this article or visit the following link: http://dx.doi.org/10.1103/PhysRevLett.113.022502

Digital Object Identifier (DOI)


Funding Information

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.

Fig 1.png (26 kB)
Figure 1

Fig 2.png (45 kB)
Figure 2

Fig 3.png (47 kB)
Figure 3

Table 1.GIF (74 kB)
Table 1

DIS_Ay_appendix_PRL_V19.pdf (75 kB)
Supplemental Material