Extraction of beam-spin asymmetries from the hard exclusive π+ channel off protons in a wide range of kinematics

We have measured beam-spin asymmetries to extract the sin phi moment A(LU)(sin phi) from the hard exclusive (e) over right arrowp -> e'n pi(+) reaction above the resonance region, for the first time with nearly full coverage from forward to backward angles in the center of mass. The A(LU)(sin phi) 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 A(LU)(sin phi) to be negative, while a sign change was observed near 90 degrees 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.