What Invariant One-Particle Multiplicity Distributions and Two-Particle   Correlations Are Telling Us about Relativistic Heavy-Ion Collisions
  We use a nine-parameter expanding source model that includes special relativity, quantum statistics, resonance decays, and freeze-out on a realistic hypersurface in spacetime to analyze invariant pi+, K+, and K- one-particle multiplicity distributions and pi+ and pi- two-particle correlations in nearly central collisions of Pb + Pb at a laboratory bombarding momentum per nucleon of 158 GeV/c. The adjustable parameters of the model are determined by minimizing chi-square with a total of 2137 data points for the five types of data considered, which leads to an acceptable value of 1.017 for chi-square per degree of freedom. Compared to earlier results obtained with this model for nearly central collisions of Si + Au at a laboratory bombarding momentum per nucleon of 14.6 GeV/c, the present results indicate that in Pb + Pb collisions the freeze-out density is somewhat lower, the freeze-out temperature is slightly higher, the source at freeze-out is somewhat larger, and the longitudinal collective velocity is very poorly determined (because of the limited experimental coverage in rapidity). For both reactions, the freeze-out temperature is less than 100 MeV and the longitudinal and transverse collective velocities-which are anti-correlated with the temperature-are substantial. We reconcile these results with those in several previous analyses that yielded a much higher freeze-out temperature of approximately 140 MeV, and finally perform two additional studies with our expanding source model. 
J. Rayford Nix, Daniel Strottman, Hubert W. van Hecke, Bernd R.   Schlei, John P. Sullivan, and Michael J. Murray