Kinematic Dependence of J/ψ Polarization Measurements in Hadronic Collisions

We emphasize the importance of performing polarization measurements in two " orthogonal " frames, such as the Collins-Soper and helicity frames. The present experimental results on J/ψ polarization, lacking in most cases such full information, need to be interpreted by means of assumptions. Assuming, for example, that the natural polarization axis is along the direction of the relative motion of the colliding partons, the seemingly contradictory J/ψ polarization results reported by E866, HERA-B and CDF consistently imply that directly produced J/ψ's are longitudinally polarized at low momentum and transversely polarized at high momentum.