First measurement of deeply virtual Compton scattering with polarized proton target

Target Spin Asymmetry is first measured in the exclusive Deeply Virtual Compton Scattering (DVCS). The asymmetry is the results of interference between the DVCS and the Bethe-Heitler (BH) process, and gives access to the Generalized Parton Distributions (GPD) H&d15; and H . The data were recorded with the CLAS detector at the Thomas Jefferson National Accelerator Facility. Both the electron beam (of energy 5.7 GeV) and the solid NH3 target were longitudinally polarized. Exclusive DVCS events were selected by requiring identifying the scattered electron, recoil proton, and detected photon. Monte-Carlo (MC) simulation is studied to estimate the background from pi0 events. The acceptance corrected single photon asymmetry is well described by the function F = p0sin&phis; + p1sin2&phis; with p 0 = 0.252 +/- 0.042stat +/- 0.020sys and p1 = -0.022 +/- 0.045stat +/- 0.021sys. This result agrees rather well with the predictions of a model of GPDs.