K${}_{\mathrm{S}}^0$ and $\mathrm{\Lambda }$ production in Pb-Pb collisions at $\sqrt{s_{\mathrm{N}\mathrm{N}}}$ = 2.76 TeV

The ALICE measurement of K${}_{\mathrm{S}}^0$ and $\mathrm{\Lambda }$ production at mid-rapidity in Pb-Pb collisions at $\sqrt{s_{\mathrm{N}\mathrm{N}}}=2.76$ TeV is presented. The transverse momentum ($p_{\mathrm{T}}$) spectra are shown for several collision centrality intervals and in the $p_{\mathrm{T}}$ range from 0.4 GeV/$c$ (0.6 GeV/$c$ for $\mathrm{\Lambda }$) to 12 GeV/$c$. The $p_{\mathrm{T}}$ dependence of the $\mathrm{\Lambda }$/K${}_{\mathrm{S}}^0$ ratios exhibits maxima in the vicinity of 3 GeV/$c$, and the positions of the maxima shift towards higher $p_{\mathrm{T}}$ 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 $p_{\mathrm{T}}$ is not observed in pp interactions at sqrt(s) = 0.9 TeV and at sqrt(s) = 7 TeV. Qualitatively, the baryon enhancement in heavy-ion collisions is expected from radial flow. However, the measured $p_{\mathrm{T}}$ spectra above 2 GeV/$c$ progressively decouple from hydrodynamical-model calculations. For higher values of $p_{\rm T}$, models that incorporate the influence of the medium on the fragmentation and hadronization processes describe qualitatively the $p_{\mathrm{T}}$ dependence of the $\mathrm{\Lambda }$/K${}_{\mathrm{S}}^0$ ratio.