Investigation of rare particle production in relativistic heavy ion collisions

During FY91 we began our investigation of rare particle production in relativistic nuclear collisions at the Brookhaven National Laboratory. We were funded for a period of one year to perform the initial experimental search, E858, to determine the level of antideuteron (bar d) production in Si+Au collisions at the AGS. We accomplished this goal with the discovery of two bar d's in the June 1990 run. We describe in this paper experiment performed and the results obtained. We performed our rare particle search at the A-1 line of the AGS. We instrumented the line with a four time-of-flight (TOF) detectors, two high pressure gas Cerenkox (ck) detectors, and four drift tube (DT) tracking detectors. The TOF detectors achieved time resolution of better than 100ps leading to a mass resolution of <15 MeV at 1 GeV. The Ck detectors were used both to suppress the large π- signal and in π/K separation at high rigidities. The DT system provided particle trajectories for all of the particles passing the trigger requirements. In this experiment we measured the π-, K-, and bar p momentum spectra at 0o for rigidities from 2 to 8 GV to a statistical accuracy of 1--3% at all settings. We found that the bar p yield as a function of target did not show any evidence for reabsorption within the interaction volume. We also found two bar d's, the first observation of complex antinuclei produced in nucleus-nucleus collisions. The bar d yield is at least an order of magnitude smaller than prediced using a simple coalescence model based on the d/p ratio from E802 and the bar p spectrum measured in our experiment