Measurement of the Target-Normal Single-Spin Asymmetry in Quasielastic Scattering from the Reaction (3)He(↑)(e,e').
We report the first measurement of the target single-spin asymmetry, A(y), in quasielastic scattering from the inclusive reaction (3)He(↑)(e,e') on a (3)He gas target polarized normal to the lepton scattering plane. Assuming time-reversal invariance, this asymmetry is strictly zero for one-photon exchange. A nonzero A(y) 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 Q(2)=0.13, 0.46, and 0.97 GeV(2). These measurements demonstrate, for the first time, that the (3)He asymmetry is clearly nonzero and negative at the 4σ-9σ level. Using measured proton-to-(3)He cross-section ratios and the effective polarization approximation, neutron asymmetries of -(1-3)% were obtained. The neutron asymmetry at high Q(2) is related to moments of the generalized parton distributions (GPDs). Our measured neutron asymmetry at Q(2)=0.97 GeV(2) agrees well with a prediction based on two-photon exchange using a GPD model and thus provides a new, independent constraint on these distributions.
Zhang, Y-W; Long, E; Mihovilovič, M; Jin, G; Allada, K; Anderson, B; Annand, JRM; Averett, T; Ayerbe-Gayoso, C; Boeglin, W; Bradshaw, P; Camsonne, A; Canan, M; Cates, GD; Chen, C; Chen, JP; Chudakov, E; De Leo, R; Deng, X; Deur, A; Dutta, C; El Fassi, L; Flay, D; Frullani, S; Garibaldi, F; Gao, H; Gilad, S; Gilman, R; Glamazdin, O; Golge, S; Gomez, J; Hansen, O; Higinbotham, DW; Holmstrom, T; Huang, J; Ibrahim, H; de Jager, CW; Jensen, E; Jiang, X; St John, J; Jones, M; Kang, H; Katich, J; Khanal, HP; King, P; Korsch, W; LeRose, J; Lindgren, R; Lu, H-J; Luo, W; Markowitz, P; Meziane, M; Michaels, R; Moffit, B; Monaghan, P; Muangma, N; Nanda, S; Norum, BE; Pan, K; Parno, D; Piasetzky, E; Posik, M; Punjabi, V; Puckett, AJR; Qian, X; Qiang, Y; Qiu, X; Riordan, S; Ron, G; Saha, A; Sawatzky, B; Schiavilla, R; Schoenrock, B; Shabestari, M; Shahinyan, A; Širca, S; Subedi, R; Sulkosky, V; Tobias, WA; Tireman, W; Urciuoli, GM; Wang, D; Wang, K; Wang, Y; Watson, J; Wojtsekhowski, B; Ye, Z; Zhan, X; Zhang, Y; Zheng, X; Zhao, B; Zhu, L; Jefferson Lab Hall A Collaboration,
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