  There are strong indications that ultra-relativistic heavy ion collisions,
produced in accelarators, lead to the formation of a new state of matter: the
quark gluon plasma (QGP). This deconfined QCD matter is expected to exist just
for very short times after the collision. All the information one can get about
the plasma is obtained from the particles that reach the detectors. Among them,
heavy vector mesons are particularly important. The abundance of $ c {\bar c}$
and $b {\bar b}$ states produced in a heavy ion collision is a source of
information about the plasma. In contrast to the light mesons, that completely
dissociate when the plasma is formed, heavy mesons presumably undergo a partial
thermal dissociation. The dissociation degree depends on the temperature and
also on the presence of magnetic fields and on the density (chemical
potential). So, in order to get information about the plasma out of the
quarkonium abundance data, one needs to resort to models that provide the
dependence of the dissociation degree on these factors. Holographic
phenomenological models provide a nice description for charmonium and
bottomonium quasi-states in a plasma. In particular, quasi-normal modes
associated with quarkonia states have been studied recently for a plasma with
magnetic fields. Here we extend this analysis of quasinormal models to the case
when charmonium and bottomonium are inside a plasma with finite density. The
complex frequencies obtained are then compared with a Breit Wigner
approximation for the peaks of the corresponding thermal spectral functions, in
order to investigate the quantitative agreement of the different descriptions
of quarkonium quasi-states.
