PRODUCTION OF PI-PLUS-OR-MINUS, K-PLUS-OR-MINUS, P, AND (P)BAR IN RELATIVISTIC AU+PT, SI+PT,AND P+PT COLLISIONS

During the recent commissioning of Au beams at the Brookhaven Alternating Gradient Synchrotron facility, experiment 886 measured production cross sections for pi+/-, K+/-, p, and pBAR in minimum bias Au + Pt collisions at 11.5A GeV/c. Invariant differential cross sections, E d3sigma/dp3, were measured at several rigidities (p/Z less-than-or-equal-to 1.8 GeV/c) using a 5.7-degrees (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, A(proj), the measured pi+/- and K+/- cross sections are nearly equal for the p + Pt and Si + Pt reactions. In contrast to this behavior, the pi- cross section measured in Au + Pt shows a significant excess beyond A(proj) scaling of the p + Pt measurement. This enhancement suggests collective phenomena contribute significantly to pi- production in the larger Au + Pt colliding system. For the Au + Pt reaction, the pi+ and K+ yields also exceed A(proj) scaling of p + Pt collisions. However, little significance can be attributed to these excesses due to larger experimental uncertainties for the positive rigidity Au beam measurements. For antiprotons, the Si + Pt and Au + Pt cross sections fall well below A(proj) scaling of the p + Pt yields indicating a substantial fraction of the nuclear projectile is ineffective for pBAR production. Comparing with p + Pt multiplicities, the Si + Pt and Au + Pt antiproton yields agree with that expected solely from ''first'' nucleon-nucleon collisions (i.e., collisions between previously unstruck nucleons). In light of expected pBAR annihilation in the colliding system, such projectile independence is unexpected without additional (projectile dependent) sources of pBAR production. In this case, the data indicate an approximate balance exists between absorption and additional sources of antiprotons. This balance is remarkable given the wide range of projectile mass spanned by these measurements.