Direct- and Resolved-Photon Threshold Resummation for Polarized High-$p_T$ Hadron Production at COMPASS

We complete our earlier study of the “direct” part of the cross section and spin asymmetry for the photoproduction process $\gamma N\to hX$ by analysing the “resolved” contribution, for which the photon couples like a hadron through its parton structure. The incident photon and nucleon are longitudinally polarized and one observes a hadron $h$ at high transverse momentum $p_T$. Soft or collinear gluon emissions generate large logarithmic threshold corrections which we resum to next-to-leading logarithmic order. We compare our results with recent spin asymmetry data by the COMPASS collaboration, highlighting the role of the fragmentation functions.