  Heavy quarkonia production is expected to be sensitive to the formation of a
quark gluon plasma (QGP). The PHENIX experiment has measured $J/\psi$
production at $\sqrt{s_{NN}}=$~200 GeV in Au+Au and Cu+Cu collisions, as well
as in reference p+p and d+Au runs. $J/\psi$'s were measured both at mid
($|y|<0.35$) and forward ($1.2<|y|<2.2$) rapidity. In this letter, we present
the A+A preliminary results and compare them to normal cold nuclear matter
expectations derived from PHENIX d+Au and p+p measurements as well as to
theoretical models including various effects (color screening, recombination,
sequential melting...).
