Observation of Exclusive Deeply Virtual Compton Scattering in Polarized Electron Beam Asymmetry Measurements

We report the first results of the beam-spin asymmetry measured in the reaction $\overrightarrow{e}p\to \mathrm{ep}\gamma$ at a beam energy of 4.25 GeV. A large asymmetry with a $\sin \phi$ modulation is observed, as predicted for the interference term of deeply virtual compton scattering (DVCS) and the Bethe-Heitler process. The amplitude of this modulation is $\alpha =0.202\mathrm{}\pm 0.028$. In leading-order and leading-twist perturbative QCD, the $\alpha$ is directly proportional to the imaginary part of the DVCS amplitude.