Polarization of charmonium in πN collisions

Measurements of the polarization of J/ψ produced in pion-nucleus collisions are in disagreement with leading twist QCD prediction were J/ψ is observed to have negligible polarization whereas theory predicts substantial polarization. We argue that this discrepancy cannot be due to poorly known structure functions nor the relative production rates of J/ψ and XJ. The disagreement between theory and experiment suggests important higher twist corrections, as has earlier been surmised from the anomalous non-factorized nuclear A-dependence of the J/ψ cross section