Production ofπ±,K±,p, andp¯ in relativistic Au+Pt, Si+Pt, andp+Pt collisions

During the recent commissioning of Au beams at the Brookhaven Alternating Gradient Synchrotron facility, experiment 886 measured production cross sections for ${\mathrm{\pi }}^{\pm }$, ${\mathit{K}}^{\pm }$, p, and p¯ in minimum bias Au+Pt collisions at 11.5A GeV/c. Invariant differential cross sections, ${\mathit{Ed}}^3$σ/${\mathit{dp}}^3$, were measured at several rigidities (p/Z≤1.8 GeV/c) using a 5.7° (fixed-angle) focusing spectrometer. For comparison, particle production was measured in minimum bias Si+Pt collisions at 14.6A GeV/c using the same apparatus and in p+Pt collisions at 12.9 GeV/c using a similar spectrometer at KEK. When normalized to projectile mass, ${\mathit{A}}_{\mathrm{proj}}$, the measured ${\mathrm{\pi }}^{\pm }$ and ${\mathit{K}}^{\pm }$ cross sections are nearly equal for the p+Pt and Si+Pt reactions. In contrast to this behavior, the ${\mathrm{\pi }}^{\mathrm{-}}$ cross section measured in Au+Pt shows a significant excess beyond ${\mathit{A}}_{\mathrm{proj}}$ scaling of the p+Pt measurement. This enhancement suggests collective phenomena contribute significantly to ${\mathrm{\pi }}^{\mathrm{-}}$ production in the larger Au+Pt colliding system.