  New results on antiparticle to particle ratios in Cu+Cu and Au+Au collisions
at sqrt(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 sqrt(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 pbar/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 sqrt(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.
