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 Alternat ing Gradient Synchrotron facility, experiment 886 measured production cross sections for pi+/-, K+/-, p, and pBAR in minimum bias Au + Pt co llisions at 11.5A GeV/c. Invariant differential cross sections, E d3si gma/dp3, were measured at several rigidities (p/Z less-than-or-equal-t o 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 co llisions at 12.9 GeV/c using a similar spectrometer at KEK. When norma lized to projectile mass, A(proj), the measured pi+/- and K+/- cross s ections are nearly equal for the p + Pt and Si + Pt reactions. In cont rast 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 significan tly 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 positi ve rigidity Au beam measurements. For antiprotons, the Si + Pt and Au + Pt cross sections fall well below A(proj) scaling of the p + Pt yiel ds indicating a substantial fraction of the nuclear projectile is inef fective 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 p reviously unstruck nucleons). In light of expected pBAR annihilation i n the colliding system, such projectile independence is unexpected wit hout additional (projectile dependent) sources of pBAR production. In this case, the data indicate an approximate balance exists between abs orption and additional sources of antiprotons. This balance is remarka ble given the wide range of projectile mass spanned by these measureme nts.