What can we learn from resonance production? 

Resonances and their decay products may interact strongly with the hadrons
of the fireball medium from the chemical freeze-out till the system breaks
up at the kinetic freeze out. In order to try understand the evolution and
expansion of this hot and dense medium we compare particle resonance yields
and spectra from elementary p+p and heavy ion collisions.

The observed decrease of the strange resonances with respect to
non-resonance in Au+Au collisions compared to the measurement in p+p
collisions suggests that medium effects are indeed present in heavy ion
collisions. These ratios, along with a knowledge of the resonance lifetime
and interaction cross-sections, mean we can place limits on the chemical
freeze-out temperature and duration of the hadronic interactions of these
collisions. Further, by studying these ratios as function of the number of
participants in Au+Au collisions we can determine the effect of the
collision volume on the rescattering and regeneration properties.