Abstract

We study the energy dependense of the transverse momentum (PT) spectra for charged pions, protons and anti-protons for An + An collisions at root(NN)-N-s = 62.4 and 200 GeV. Data are presented at mid-rapidity (broken vertical bar y broken vertical bar 0.5) for 0.2 PT 12 GeV/c. In the intermediate PT region (2 PT 6 GeV/c), the nuclear modification factor is higher at 62.4 GeV than at 200 GeV, while at higher PT (PT > 7 GeV/c) the modification is similar for both energies. The p/pi(+) and (p) over bar/pi(-) ratios for central collisions at root(NN)-N-s = 62.4 GeV peak at PT similar or equal to 2 GeV/c. In the PT range where recombination is expected to dominate, the p/pi(+) ratios at 62.4 GeV are larger than at 200 GeV, while the (p) over bar/pi(-) ratios are smaller. For PT > 2 GeV/c, the (p) over bar/pi(-) ratios at the two beam energies are independent of P-T and centrality indicating that the dependence of the (p) over bar/pi(-) ratio on P-T does not change between 62.4 and 200 GeV. These findings challenge various models incorporating jet quenching and/or constituent quark coalescence. (C) 2007 Elsevier B.V. All rights reserved.