Two-particle correlation from a relativistic fluid with a first order   phase transition
  We numerically calculate two-particle correlation functions of CERN-SPS 158   A GeV Pb+Pb central collisions based on a (3+1)-dimensional relativistic hydrodynamics with a first order phase transition. We analyze the pair momentum dependence of pion source sizes extracted from the   Yano-Koonin-Podgoretski\u{\i} (YKP) parametrization which is expected to give the source sizes directly. We find that, even in the case of the first order phase transition, the collective expansion and surface dominant freeze-out of the fluid naturally lead to the opaque source for which the interpretation of the temporal source parameter as the emission duration breaks down. 
Kenji Morita, Shin Muroya, Hiroki Nakamura and Chiho Nonaka