Pion, kaon, and proton production in central Pb-Pb collisions at root s(NN)=2.76 TeV

Abstract

In this Letter we report the first results on π ± , K± , p, and ¯ p production at midrapidity ( | y | < 0.5 ) in central Pb-Pb collisions at √ s NN = 2.76 TeV , measured by the ALICE experiment at the LHC. The pTdistributions and yields are compared to previous results at √ s NN = 200 GeV and expectations from hydrodynamic and thermal models. The spectral shapes indicate a strong increase of the radial flow velocity with √ s NN , 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.