Photoproduction of large-pThadrons by polarized beam and target

The production at large transverse momentum ($p_T$) of hadrons by a polarized photon beam on a longitudinally polarized proton target is studied. The contributions due to the structure of the photon are taken into account and discussed. In certain kinematic domains cross sections and event rates sizable enough for successful experiments are predicted and single hadron production is shown to be a good probe of the size of the polarized gluon distribution. A particularly clean probe is found to be a special combination of cross sections for the production of two large-$p_T$ hadrons. The feasibility of high-energy polarized photon beams is also discussed.