J/$\psi$ production measurements by the PHENIX experiment at RHIC

Understand

Measurements of J/$\psi$ production by the PHENIX experiment in p+p, d+Au, Cu+Cu and Au+Au collisions at $\sqrt{s_{NN}}$=200 GeV are reviewed.

• The results show a suppression beyond what can be explained by cold nuclear matter effects in the most central Au+Au and to a lesser extent in Cu+Cu collisions.
• In addition, the suppression observed at mid rapidity in Au+Au is smaller than at forward rapidity, a tendency opposite to what is expected from the higher energy density at mid rapidity.
• Regeneration, a possible explanation, can be tested by measuring the elliptic flow parameter v$_2$ of J/$\psi$.