SEMIINCLUSIVE PION-PHOTOPRODUCTION AT LARGE TRANSVERSE-MOMENTA

We show that very high momentum transfer semi-inclusive photoproductio n of pions from nucleons, gammap --> piX, is dominated by a subprocess where the pions are produced directly. Although the ''direct subproce ss'' may be thought of as a limiting case of a quark fragmentation sub process, it is an exclusive process at the quark level, fully calculab le using perturbative QCD, and thus distinct from the usual thinking a bout fragmentation processes. Our numerical results, concentrating on neutral pions, indicate that the direct subprocess is dominant at pion transverse momenta slightly higher than those already measured. Incid entally, the integral over the pion distribution amplitude in the pres ent case is the same as that for the pion electromagnetic form factor, but the momentum transfers involved correspond to measuring the pion form factor at momentum transfers up to several hundred GeV2.