Antimatter and matter production in heavy ion collisions at CERN (The NEWMASS experiment NA52)

Besides the dedicated search for strangelets NA52 measures light (anti)part icle and (anti)nuclei production over a wide range of rapidity. Compared to previous runs the statistics has been increased in the 1998 run by more th an one order of magnitude for negatively charged objects at different spect rometer rigidities. Together with previous data taking at a rigidity of -20 GeV/c we obtained 10(6) (p) over bar, 10(3) (d) over bar and two (He-3) ov er bar without centrality requirements. We measured nuclei and antinuclei ( p, d, (p) over bar, (d) over bar) near midrapidity covering an impact param eter range of b similar to 2-12 fm. Our results strongly indicate that nucl ei and antinuclei are mainly produced via the coalescence mechanism. Howeve r, the centrality dependence of the antibaryon to baryon ratios shows that antibaryons are diminished due to annihilation and breakup reactions in the hadron dense environment. The volume of the particle source extracted from coalescence models agrees with results from pion interferometry for an exp anding source. The chemical and thermal freeze-out of nuclei and antinuclei appear to coincide with each other and with the thermal freeze-out of hadr ons.