Rescattering Eeects in Quarkonium Production 1

revised November 17, 1997 Rescattering E ects in Quarkonium Production1 Paul Hoyer and St ephane Peign e Nordita Blegdamsvej 17, DK{2100 Copenhagen , Denmark Abstract We study c and J= hadroproduction induced by multiple scattering o xed 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 c and of the cross section for the J= . The J= provides an interesting example of soft rescattering e ects occurring inside a hard vertex. We also explain the qualitative di erence between the transverse momentum broadening of the J= and of the observed in collisions on nuclei. We point out that rescattering from spectators produced by beam and target parton evolution may have important e ects in J= production.