  We study eta_c and J/psi hadroproduction induced by multiple scattering off
fixed centres in the target. We determine the minimum number of hard
scatterings required and show that additional soft scatterings may 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 interesting example of soft
rescattering effects occurring inside a hard vertex. We also explain the
qualitative difference between the transverse momentum broadening of the J/psi
and of the Upsilon observed in collisions on nuclei. We point out that
rescattering from spectators produced by beam and target parton evolution may
have important effects in J/psi production.
