Physical Review Letters
172502 (6 pages)
We report the first measurement of the target single-spin asymmetry, Ay, in quasielastic scattering from the inclusive reaction ³He↑(e, e') on a ³He gas target polarized normal to the lepton scattering plane. Assuming time-reversal invariance, this asymmetry is strictly zero for one-photon exchange. A nonzero Ay can arise from the interference between the one-and two-photon exchange processes which is sensitive to the details of the substructure of the nucleon. An experiment recently completed at Jefferson Lab yielded asymmetries with high statistical precision at Q2 = 0.13, 0.46, and 0.97 GeV2. These measurements demonstrate, for the first time, that the 3He asymmetry is clearly nonzero and negative at the 4σ-9σ level. Using measured proton-to-3He cross-section ratios and the effective polarization approximation, neutron asymmetries of -(1-3)% were obtained. The neutron asymmetry at high Q2 is related to moments of the generalized parton distributions (GPDs). Our measured neutron asymmetry at Q2 = 0.97 GeV2 agrees well with a prediction based on two-photon exchange using a GPD model and thus provides a new, independent constraint on these distributions.
Original Publication Citation
Zhang, Y. W., Long, E., Mihovilovic, M., Jin, G., Allada, K., Anderson, B., . . . Jefferson Lab Hall, A. C. (2015). Measurement of the target-normal single-spin asymmetry in quasielastic scattering from the reaction ³He↑(e, e'). Physical Review Letters, 115(17), 172502. doi:10.1103/PhysRevLett.115.172502
Zhang, Y. W.; Long, E.; Mihoviloviĉ, M.; Gin, G.; Canan, M; Golge, S.; and Schiavilla, R., "Measurement of the Target-Normal Single-Spin Asymmetry in Quasielastic Scattering from the Reaction ³He↑(e, e')" (2015). Physics Faculty Publications. 142.