We present the results from the BRAHMS experiment at the Relativistic Heavy Ion Collider (RHIC) for the ¹⁹⁷Au + ¹⁹⁷Au reaction at \sqrt {s_NN} = 130 GeV and \sqrt {s_NN} = 200 GeV. The main focus is here on the determination of the pseudorapidity distribution of charged particles produced in the reaction as a function of pseudorapidity and centrality and on the measurement of the anti-proton to proton ratio as a function of rapidity. Our measurements show that up to 3860 and 4630 charged particles are produced in the top 5% central collisions and that the number of produced particles per participating nucleon pair exceeds values from p + p collisions by about 40% and 50% for \sqrt {s_NN} = 130 GeV and \sqrt {s_NN} = 200 GeV, respectively. The N(\overline {p})/N(p) ratio at mid-rapidity is found to be 0.64 \pm 0.06 for the lower, and around 0.75 for the top RHIC energy. These values are the highest observed so far in nucleus--nucleus reaction and show a tendency for matter and antimatter to balance at mid-rapidity as the bombarding energy increases, they also indicate that the net-bayron free mid-rapidity plateau (Bjorken limit) is not reached at this RHIC energies. It is also shown that current models are not able to consistently describe the particle multiplicities and the baryonic ratios.

PACS numbers: 25.75.--q, 25.75.Dw