  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.
