Antiparticle to particle ratios and identified hadron spectra in Cu+Cu and Au+Au collisions

New results on antiparticle to particle ratios in Cu+Cu and Au+Au collisions at √ s NN = 62.4 and 200 GeV from the PHOBOS experiment at RHIC are presented. Transverse momentum spectra of pions, kaons, protons and antiprotons from Au+Au collisions at √ s NN = 62.4 GeV close to mid-rapidity are also discussed. Antiparticle to particle ratios are found to be remarkably independent of the collision centrality in both colliding systems. The collision energy dependence of the p/p ratios is very significant in Cu+Cu collisions. Baryons are found to have substantially harder transverse momentum spectra than mesons. The pT region in which the proton to pion ratio reaches unity in central Au+Au collisions at √ s NN = 62.4 GeV fits into a smooth trend as a function of collision energy. The observed particle yields at very low pT are comparable to extrapolations from higher pT for kaons, protons and antiprotons. The net proton yield at mid-rapidity is found to be proportional to the number of participant nucleons in Au+Au collisions at 62.4 and 200 GeV energies. PACS numbers: 25.75.-q, 13.85.Ni, 21.65.+f Submitted to: J. Phys. G: Nucl. Phys. Particle ratios and identified hadron spectra from PHOBOS 2