Mass number scaling in ultra-relativistic nuclear collisions from a hydrodynamical approach

We study the different nucleus-nucleus collisions, O+Au, S+S, S+Ag, S+Au and Pb+Pb, at the CERN-SPS energy in a one-fluid hydrodynamical approach using a parametrization based on baryon stopping in terms of the thickness of colliding nuclei. Good agreement with measured particle spectra is achieved. We deduce the mass number scaling behaviour of the initial energy density. We find that the equilibration time is nearly independent of the size of the colliding nuclei. Received: 23 January 1998 / Revised version: 8 May 1998 / Published online: 12 August 1998