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Semiexclusive Processes: A different way to probe hadron structure

Hard semiexclusive processes provide an opportunity to design effective currents to probe specific parton distributions and to probe in leading order parton distributions that fully inclusive reactions probe only via higher order corrections. High transverse momentum pion photoproduction is an example of a such a process. We discuss the perturbative and soft processes that contribute, and show how regions where perturbative processes dominate can give us the parton structure information. Polarized initial states are needed to get information on polarization distributions. Current polarization asymmetry data is mostly in the soft region. However, with somewhat higher energy, determining the polarized gluon distribution using hard pion photoproduction appears quite feasible.