Extraction of Beam-Spin Asymmetries from the Hard Exclusive π+ Channel off Protons in a Wide Range of Kinematics
Physical Review Letters
We have measured beam-spin asymmetries to extract the sinφ moment ALUsinφ from the hard exclusive e→p→e′nπ+ reaction above the resonance region, for the first time with nearly full coverage from forward to backward angles in the center of mass. The ALUsinφ moment has been measured up to 6.6 GeV2 in -t, covering the kinematic regimes of generalized parton distributions (GPD) and baryon-to-meson transition distribution amplitudes (TDA) at the same time. The experimental results in very forward kinematics demonstrate the sensitivity to chiral-odd and chiral-even GPDs. In very backward kinematics where the TDA framework is applicable, we found ALUsinφ to be negative, while a sign change was observed near 90° in the center of mass. The unique results presented in this Letter will provide critical constraints to establish reaction mechanisms that can help to further develop the GPD and TDA frameworks.
Diehl, S., Joo, K., Kim, A., Avakian, H., Kroll, P., Park, K., Riser, D., Semenov-Tian-Shansky, K., Tezgin, K., Adhikari, K., Adhikari, S., Amaryan, M., Angelini, G., Asryan, G., Atac, H., Barion, L., & Battaglieri, M. (2020). Extraction of Beam-Spin Asymmetries from the Hard Exclusive π+ Channel off Protons in a Wide Range of Kinematics. Physical Review Letters, 125 (18). https://doi.org/10.1103/PhysRevLett.125.182001