Fine-Tuning Two-Particle Interferometry II: Opacity Effects
  We present a model study of single-particle spectra and two-particle Bose-Einstein correlations for opaque sources. We study the transverse mass dependence of the correlation radii R_\perp, R_\parallel and R_0 in the YKP parametrization and find a strong sensitivity of the temporal radius parameter R_0^2 to the source opacity. A simple comparison with the published data from 158 A GeV/c Pb+Pb collisions at CERN indicates that the pion source created in these collisions emits particles from the whole reaction volume and is not opaque. For opaque sources we find certain regions of inapplicability of the YKP parametrization which can be avoided by a slightly different parametrization for the correlator. The physical meaning of the modified parameters is briefly discussed. 
Boris Tomasik and Ulrich Heinz (Regensburg)