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The spin asymmetry in the photoproduction of pairs of high transverse momentum hadrons at HERMES

Results from the HERMES experiment at the DESY Laboratory in Germany are presented on the longitudinal asymmetry in the photoproduction of pairs of oppositely charged hadrons with high transverse momentum. A negative asymmetry is determined in contrast to the positive asymmetries typically measured in deep-inelastic scattering from protons. Monte Carlo studies indicate that the photon-gluon process contributes substantially in this kinematical domain. Using this information, the negative asymmetry can then be interpreted to arise from a positive gluon polarization in the proton.