Measurement of the Target-Normal Single-Spin Asymmetry in Quasi-Elastic Scattering from the Reaction ³He^uparrow(e,e^prime)

Y.-W. Zhang , E. Long , M. Mihovilovi\v{c} , G. Jin , K. Allada , B. Anderson , J. R. M. Annand , T. Averett

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W. Boeglin P. Bradshaw A. Camsonne M. Canan G. D. Cates C. Chen J. P. Chen E. Chudakov R. De Leo X. Deng A. Deur C. 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. \v{S}irca R. Subedi V. Sulkosky W. A. Tobias W. Tireman G. M. Urciuoli D. Wang K. Wang Y. Wang J. Watson B. Wojtsekhowski Y. Ye Z. Ye X. Zhan Y. Zhang X. Zheng B. Zhao L. Zhu

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classification ⚛️ nucl-ex

keywords asymmetryexchangeneutronscatteringasymmetriesdistributionsfirsthigh

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We report the first measurement of the target single-spin asymmetry, $A_y$, in quasi-elastic scattering from the inclusive reaction $^3$He$^{\uparrow}(e,e^\prime)$ 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 non-zero $A_y$ can arise from the interference between the one- and two-photon exchange processes which is sensitive to the details of the sub-structure 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 non-zero and negative with a statistical significance of (8-10)$\sigma$. 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.

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Measurement of the Target-Normal Single-Spin Asymmetry in Quasi-Elastic Scattering from the Reaction ³He^uparrow(e,e^prime)

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