Numerical analysis of a two-pion correlation function based on a hydrodynamical model

We will numerically investigate the two-particle correlation function of the CERN-SPS 158A GeV Pb+Pb central collisions in detail based on a (3+1)-dimensional relativistic hydrodynamical model with first order phase transition. We use the Yano-Koonin-Podgoretskii (YKP) parametrization as well as the usual Cartesian parametrization and analyze the pair momentum dependence of the Hanbury Brown-Twiss radii extracted from the parametrizations. We find that the interpretation of the temporal radius parameter as the time duration in the YKP parametrization is not available for the hydrodynamical model where the source became opaque naturally because of expansion and surface dominant freeze-out. Finally, the effect of the phase transition on the source opacity is also discussed.