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 $p_{\perp }$-averaged production of charmonium states in $\pi N$ collisions at fixed target energies. The data on the relative production rates of $\text{jp}$ and ${\chi }_J$ is found to disagree with leading twist QCD. The polarization of the $\text{jp}$ 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.

Comments: 19 pages