LOW FREEZE-OUT TEMPERATURE AND HIGH COLLECTIVE VELOCITIES IN RELATIVISTIC HEAVY-ION COLLISIONS

On the basis of a nine-parameter expanding source model that includes special relativity, quantum statistics, resonance decays, and freeze-o ut on a realistic hypersurface in spacetime, we analyze in detail inva riant pi(+) pi(-), K+, and K- one-particle multiplicity distributions and pi(+) and K+ two-particle correlations in nearly central collision s of Si+Au at p(lab)/A = 14.6 GeV/c. By considering separately the one -particle data and the correlation data, we find that the central bary on density, nuclear temperature, transverse collective velocity, longi tudinal collective velocity, and sourer velocity are determined primar ily by one-particle multiplicity distributions and that the transverse radius, longitudinal proper time, width in proper time, and pion inco herence fraction are determined primarily by two-particle correlations . By considering separately the pion data and the kaon data, we find t hat although the pion freeze-out occurs somewhat later than the kaon f reeze-out, the 99% confidence-level error bars associated with the two freeze-outs overlap. By constraining the transverse freeze-out to the same source time for all points with the same longitudinal position a nd by allowing a more flexible freeze-out in the longitudinal directio n, we find that the precise shape of the freeze-out hypersurface is re latively unimportant. By regarding the pion and kaon one-particle data to be unnormalized, we find that the nuclear temperature increases sl ightly, but that its uncertainty increases substantially. By including proton one-particle data (which are contaminated by spectator protons ), we find that the nuclear temperature increases slightly. These deta iled studies confirm our earlier conclusion based on the simultaneous consideration of the pion and kaon one-particle and correlation data t hat the freeze-out temperature is less than 100 MeV and that both the longitudinal and transverse collective velocities-which an anticorrela ted with the temperature-are substantial. We also discuss the flaws in several previous analyses that yielded a much higher freeze-out tempe rature of approximately 140 MeV for both this reaction and other react ions involving heavier projectiles and/or higher bombarding energies. [S0556-2813(98)04709-8].