Rapidity dependence of antiproton-to-proton ratios in Au + Au collisions at √sNN = 130 GeV

Measurements, with the BRAHMS detector, of the antiproton-to-proton ratio at midrapidities and forward rapidities, are presented for Au + Au reactions at √sNN = 130 GeV, and for three different collision centralities. For collisions in the 0%-40% centrality range, we find N (p̄) / N (p) = 0.64 ± 0.04(stat) ± 0.06(syst) at y ≈ 0, 0.66 ± 0.03 ± 0.06 at y ≈ 0.7, and 0.41 ± 0.04 ± 0.06 at y ≈ 2. The ratios are found to be nearly independent of collision centrality and transverse momentum. The antiproton and proton rapidity densities vary differently with rapidity, and indicate a significant degree of collision transparency, although a net-baryon free midrapidity plateau (Bjorken limit) is not yet reached.