We report the first results of the beam-spin asymmetry measured in the reaction ep→epγ at a beam energy of 4.25 GeV. A large asymmetry with a sinφ 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 α=0.202±0.028. In leading-order and leading-twist perturbative QCD, the α is directly proportional to the imaginary part of the DVCS amplitude.
Physical Review Letters
Stepanyan, S.; Biselli, Angela; and CLAS Collaboration, "Observation of Exclusive Deeply Virtual Compton Scattering in Polarized Electron Beam Asymmetry Measurements" (2001). Physics Faculty Publications. 104.
S. Stepanyan et al. [CLAS Collaboration], "Observation of Exclusive Deeply Virtual Compton Scattering in Polarized Electron Beam Asymmetry Measurements", Physical Review Letters 87.18 (2001) DOI: 10.1103/PhysRevLett.87.182002