Centrality dependence of $\psi\prime$ over $J/\psi$ : a signal of QGP

Abstract

If nuclear collisions lead to QGP formation then the ratio of $\psi\prime$ over $J/\psi$ will remain constant with $E_T$ as both $J/\psi$ and $\psi\prime$ are melted in the QGP. On the other hand, if hot hadronic matter is produced, the ratio will continually fall with $E_T$, as $\psi\prime$'s are more suppressed in hadronic matter than the $J/\psi$'s. From the existing NA50 Pb+Pb data, we have constructed the ratio $\sigma(\psi\prime)/\sigma(J/\psi)$, as a function of $E_T$. The ratio give indication of QGP formation, but definite conclusion can not be reached. We have also given the prediction for the ratio at RHIC energy. If QGP is formed at RHIC, it could be detected from the ratio.