Hard exclusive reactions are the tool to learn about generalized parton distributions, which provide a more complete parametrization of the nucleon than the ordinary parton distribution functions. Recent measurements by the HERMES collaboration of the exclusive production of photons, i.e., Deeply-Virtual Compton Scattering, are summarized and compared to model calculations, focusing on the measurements and model comparisons relevant to the extraction of quark orbital angular momentum and on the measurements on heavy nuclei.
Comment: 8 pages, 12 figures, Invited talk presented at the workshop on Exclusive Processes at High Momentum Transfer, Newport News, Virginia USA, May 2007; to appear in the proceedings