Hadroproduction and Polarization of Charmonium
  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 $\jp$ and $\chi_J$ is found to disagree with leading twist QCD. The polarization of the $\jp$ 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. 
M. V\"anttinen, P. Hoyer, S. J. Brodsky and W.-K. Tang