Scanning the quark-gluon plasma with charmonium - art. no. 112302

We suggest the variation of charmonium production rate with Feynman x(F) in heavy ion collisions as a novel and sensitive probe for the properties of the created matter. Final state interactions with the comoving matter creat e a minimum at x(F) = 0, which is especially deep and narrow if a quark-glu on plasma is formed. While a strong effect is predicted at SPS. at the RHIC energy it overlaps with the expected peak formed by shadowing effects and needs comparison with pA data. We predict a steep dependence on centrality and suggest that this new probe is complementary to the dependence on trans verse energy, and is more sensitive to a scenario of final state interactio ns.