Measurements, with the BRAHMS detector, of the antiproton-to-proton ratio at midrapidities and forward rapidities, are presented for Au + Au reactions at roots(NN) = 130 GeV, and for three different collision centralities. For collisions in the 0%-40% centrality range, we find N((p) over bar)/N(p) = 0.64 +/- 0.04((stat)) +/- 0.06((syst)) at y approximate to 0, 0.66 +/- 0.03 +/- 0.06 at y approximate to 0.7, and 0.41 +/- 0.04 +/- 0.06 at y approximate to 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.
Sanders, Stephen J. Rapidity dependence of antiproton-to-proton ratios in Au+Au collisions at root s(NN)=130 GeV. PHYSICAL REVIEW LETTERS. SEP 10 2001. 87(11): art. no.-112305.