RESCATTERING EFFECTS IN QUARKONIUM PRODUCTION

We study eta(c) and J/psi hadroproduction induced by multiple scatteri ng off fixed centers in the target. We determine the minimum number of hard scatterings required and show that additional soft scatterings m ay be factorized, at the level of the production amplitude for the eta (c) and of the cross section for the J/psi. The J/psi provides an inte resting example of soft rescattering effects occurring inside a hard v ertex. We also explain the qualitative difference between the transver se momentum broadening of the J/psi and of the Y observed in collision s on nuclei. We point out that rescattering from spectators produced b y beam and target parton evolution may have important effects on J/psi production.