J/ψ production at the Tevatron and RHIC from s-channel cut

We report on our recent evaluation of the s-channel cut contribution to J/ψ hadroproduction. We show that it is likely significantly larger than the usual cut contribution of the colour-singlet model (CSM), which is known to underestimate the experimental measurements. Here the s-channel cut develops for configurations with off-shell quarks in the bound state. A correct treatment of its contribution requires the introduction of a fourpoint function, partially constrained by gauge invariance and limiting behaviours at small and large momenta. When the unconstrained degrees of freedom are fixed to reproduce the Tevatron data, we show that RHIC data are remarkably well reproduced down to very low transverse momenta PT without need of resummation of initial-state gluon effects. This unique feature might be typical of s-channel cut contribution.