Internal Charmonium Evolution in the Quark-Gluon Plasma

We employ a time-dependent Schr\"odinger equation to study the evolution of a $c\bar c$ dipole in a quark-gluon plasma (QGP). Medium effects on the heavy-quark potential in the QGP are found to significantly affect the timescales of the internal evolution of the dipole. Color-screening can enhance the overlap of the expanding wavepackage with excited states at high temperature, while it is reduced at lower temperatures where the dipole favors the formation of the charmonium ground state. We investigate the consequences of this mechanism on the double ratio of charmonium nuclear modification factors, $R_{AA}^{\psi(2S)}/R_{AA}^{J/\psi}$, in heavy-ion collisions. The impact of the transition mechanisms on this ratio turns out to be rather sensitive to the attractive strength of the potential, and to its temperature dependence.