Hadroproduction and polarization of charmonium.

Abstract

In the limit of heavy-quark mass, the production cross section and polarization of quarkonia can be calculated in perturbative QCD. We study the ${\mathit{p}}_{\mathrm{\ensuremath{\perp}}}$-averaged production of charmonium states in \ensuremath{\pi}N collisions at fixed target energies. The data on the relative production rates of J/\ensuremath{\psi} and ${\mathrm{\ensuremath{\chi}}}_{\mathit{J}}$ are found to disagree with leading twist QCD. The polarization of the J/\ensuremath{\psi} indicates that the discrepancy is not due to poorly known parton distributions nor to the size of higher order effects (K factors). Rather, the disagreement suggests important higher twist corrections, as has been surmised earlier from the nuclear target A dependence of the production cross section.