Measurement of the Target-Normal Single-Spin Asymmetry in Quasielastic Scattering from the Reaction He 3 ↑ (e,e′)

Y. W. Zhang, E. Long, M. Mihovilovič, G. Jin, K. Allada, B. Anderson, J. R.M. Annand, T. Averett, C. Ayerbe-Gayoso, W. Boeglin, P. Bradshaw, A. Camsonne, M. Canan, G. D. Cates, C. Chen, J. P. Chen, E. Chudakov, R. De Leo, X. Deng, A. DeurC. Dutta, L. El Fassi, D. Flay, S. Frullani, F. Garibaldi, H. Gao, S. Gilad, R. Gilman, O. Glamazdin, S. Golge, J. Gomez, O. Hansen, D. W. Higinbotham, T. Holmstrom, J. Huang, H. Ibrahim, C. W. De Jager, E. Jensen, X. Jiang, J. St John, M. Jones, H. Kang, J. Katich, H. P. Khanal, P. King, W. Korsch, J. Lerose, R. Lindgren, H. J. Lu, W. Luo, P. Markowitz, M. Meziane, R. Michaels, B. Moffit, P. Monaghan, N. Muangma, S. Nanda, B. E. Norum, K. Pan, D. Parno, E. Piasetzky, M. Posik, V. Punjabi, A. J.R. Puckett, X. Qian, Y. Qiang, X. Qiu, S. Riordan, G. Ron, A. Saha, B. Sawatzky, R. Schiavilla, B. Schoenrock, M. Shabestari, A. Shahinyan, S. Širca, R. Subedi, V. Sulkosky, W. A. Tobias, W. Tireman, G. M. Urciuoli, D. Wang, K. Wang, Y. Wang, J. Watson, B. Wojtsekhowski, Z. Ye, X. Zhan, Y. Zhang, X. Zheng, B. Zhao, L. Zhu

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Abstract

We report the first measurement of the target single-spin asymmetry, Ay, in quasielastic scattering from the inclusive reaction He3↑(e,e′) on a He3 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 0.97GeV2. These measurements demonstrate, for the first time, that the He3 asymmetry is clearly nonzero and negative at the 4σ-9σ level. Using measured proton-to-He3 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=0.97GeV2 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 languageEnglish
Article number172502
JournalPhysical Review Letters
Volume115
Issue number17
DOIs
StatePublished - 22 Oct 2015

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