MEASURING POLARIZED GLUON AND QUARK DISTRIBUTIONS WITH MESON PHOTOPRODUCTION - ART. NO. 054007

We calculate polarization asymmetries in the photoproduction of high t ransverse momentum mesons, focusing on charged pions, considering the direct, fragmentation, and resolved photon processes. The results at v ery high meson momentum measure the polarized quark distributions and are sensitive to differences among the existing models. The results at moderate meson momentum are sensitive to the polarized gluon distribu tion and can provide a good way to measure it. Suitable data may come as a by-product of deep inelastic experiments to measure g(1) or from dedicated experiments. [S0556-2821(98)05015-2].