Pion interferometry testing the validity of hydrodynamical models

We show how a joint analysis of the transversal momentum spectrum, rapidity distributions and the interferometrical correlator can test and distinguish between different models of hydrodynamical expansion of matter. Our study shows that the hydrodynamical picture is inadequate for minimum bias events at CERN ISR energies. On the other hand, current data on ultra-relativistic nucleus-nucleus collisions are shown to be consistent with the existence of hydrodynamical flows in the matter formed in these processes. More complete and accurate interferometrical data is demanded for clarifying the matter evolution in time and space. (orig.)