Inelastic $J/\Psi$ Photoproduction off Nuclei: Gluon Enhancement or   Double Color Exchange?
  The nuclear enhancement observed in inelastic photoproduction of $J/\Psi$ should not be interpreted as evidence for an increased gluon density in nuclei. The nuclear suppression of the production rate due to initial and final state interactions is calculated and a novel two-step color exchange process is proposed, which is able to explain the data. 
J. Huefner (Un. Heidelberg), B.Z. Kopeliovich (MPI Heidelberg), Al.B.   Zamolodchikov (Un. Montpellier)