Hadronic phase space density and chiral symmetry restoration in relativistic heavy ion collisions

The effect of altered hadron masses is studied for its effect with regard t o final-state hadronic observables. It is shown that the final phase space densities of pions and kaons, which can be inferred experimentally, are sen sitive to in-medium properties of the excited matter at earlier stages of t he collision, but that the sensitivity is significantly moderated by intera ctions that change the effective numbers of pions and kaons during the latt er part of the collision. [S0556-2813(99)07105-8].