E683 is an experiment in gamma-p goes to jets, and there are two main types of photoproduction at lowest order. The most interesting is direct coupling, in which the photon couples directly to a parton from the proton. This has two advantages. First, the entire photon is absorbed, leaving no beam fragments to contaminate your signal. Second, the entire photon is absorbed, meaning the entire beam energy is absorbed, leading to harder events.
Resolved coupling occurs when the photon appears as a virtual quark-anti-quark pair.
At our energies, the leading order prediction is that each process contributes about equally to our cross-section.
Greg Morrow morrow@physics.rice.edu