Hadro-Production of Quarkonia in Fixed Target Experiments

Abstract

In this talk I review the recent progress made in the calculations of quarkonia production in fixed target experiments. NRQCD organizes the calculations in a systematic expansion in $α_s$ and $v$, the relative velocity between the heavy quarks. Within this formalism there are octet contributions which are not included in the color singlet model. These contributions depend upon unknown matrix elementsof local operators which are fit to the data. Using these fits, there are several predictions which do indeed improve agreement with the data. However, the prediction for the polarization of the produced states as well as the ratio of the $χ_1$ to $χ_2$ cross sections differ substantially from the data for the case of pion beams. Possible large corrections from higher twist effects are discussed as is the issue of the the proper choice of masses.