Centrality dependence of the nuclear modification factor of charged pions, kaons, and protons in Pb-Pb collisions at root s(NN)=2.76 TeV

Abstract

Transverse momentum (p(T)) spectra of pions, kaons, and protons up to p(T) = 20 GeV/c have been measured in Pb-Pb collisions at root s(NN) = 2.76 TeV using the ALICE detector for six different centrality classes covering 0%-80%. The proton-to-pion and the kaon-to-pion ratios both show a distinct peak at p(T) approximate to 3 GeV/c in central Pb-Pb collisions that decreases for more peripheral collisions. For p(T) GT 10 GeV/c, the nuclear modification factor is found to be the same for all three particle species in each centrality interval within systematic uncertainties of 10%-20%. This suggests there is no direct interplay between the energy loss in the medium and the particle species composition in the hard core of the quenched jet. For p(T) LT 10 GeV/c, the data provide important constraints for models aimed at describing the transition from soft to hard physics.