Pion, Kaon, and Proton Production in Central Pb--Pb Collisions at sqrt{s_NN} = 2.76 TeV

Abstract

In this Letter we report the first results on π±, K±, p and pp¯¯¯ production at mid-rapidity (|y|<0.5) in central Pb-Pb collisions at sNN−−−√ = 2.76 TeV, measured by the ALICE experiment at the LHC. The pT distributions and yields are compared to previous results at sNN−−−√ = 200 GeV and expectations from hydrodynamic and thermal models. The spectral shapes indicate a strong increase of the radial flow velocity with sNN−−−√, which in hydrodynamic models is expected as a consequence of the increasing particle density. While the K/π ratio is in line with predictions from the thermal model, the p/π ratio is found to be lower by a factor of about 1.5. This deviation from thermal model expectations is still to be understood.