K-S(0) and Lambda Production in Pb-Pb Collisions at root s(NN)=2: 76 TeV

Abstract

The ALICE measurement of K-S(0) and Lambda production at midrapidity in Pb-Pb collisions at root sNN = 2.76 TeV is presented. The transverse momentum (p(T)) spectra are shown for several collision centrality intervals and in the p(T) range from 0: 4 GeV/c (0: 6 GeV/c for Lambda) to 12 GeV/c. The p(T) dependence of the Lambda/K-S(0) ratios exhibits maxima in the vicinity of 3 GeV/c, and the positions of the maxima shift towards higher p(T) with increasing collision centrality. The magnitude of these maxima increases by almost a factor of three between most peripheral and most central Pb-Pb collisions. This baryon excess at intermediate p(T) is not observed in pp interactions at root s = 0.9 TeV and at root s = 7 TeV. Qualitatively, the baryon enhancement in heavy-ion collisions is expected from radial flow. However, the measured p(T) spectra above 2 GeV/c progressively decouple from hydrodynamical-model calculations. For higher values of p(T), models that incorporate the influence of the medium on the fragmentation and hadronization processes describe qualitatively the p(T) dependence of the Lambda/K-S(0) ratio.