SESZIONE DI TORINO
More than 20 years ago Matsui and Satz proposed the J/psi suppression due to Debye screening as a signature of the onset of deconfinement, triggering a lot of experimental efforts to measure its yields in high-energy nucleus-nucleus collisions. On the theory side in the last few years quite precise lattice data became available, both for the QQbar free-energies and the in-medium correlators of quarkonia. This, hopefully, should make possible a more solid quantitative study of the problem. Quite surprisingly the spectral functions extracted from the temporal correlators of quarkonia turned out to display well-defined peaks, reflecting the presence of bound/resonant states till temperatures of order 2T_c, at least in the s-wave channels. Various attempts were done in order to interpret both the above large melting temperatures and the charmonia correlators themselves in terms of screened potential models. The latter represents a quite economic way of accounting for medium effects, which is often employed to describe the interaction between charged particles in a polarizable medium. However, beside checking the numerical agreement of the findings obtained in the two approaches, it would be of interest to see such a medium-modified QQbar potential arising from a first principle calculation. Different papers appeared quite recently addressing this issue. Here we wish to answer a few very general questions concerning the description of a QQbar pair in a hot plasma: whether it is possible to give a solid theoretical basis to the concept of an effective in-medium potential; if so, which is its link with the QQbar free-energy obtained from the imaginary-time propagator of a static pair of heavy quarks; finally, whether, beside the screening of the interaction it is possible, within the same framework, to account also for other effects, like the collisional damping.

DATA: 15-12-2008