In this Letter we report the first results on ${\pi }^{\pm }$, $K^{\pm }$, $p$, and $\overline{p}$ production at midrapidity ($|y|<0.5$) in central Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=2.76\mathrm{TeV}$, measured by the ALICE experiment at the LHC. The $p_{\mathrm{T}}$ distributions and yields are compared to previous results at $\sqrt{s_{\mathrm{NN}}}=200\mathrm{GeV}$ and expectations from hydrodynamic and thermal models. The spectral shapes indicate a strong increase of the radial flow velocity with $\sqrt{s_{\mathrm{NN}}}$, which in hydrodynamic models is expected as a consequence of the increasing particle density. While the $K/\pi$ ratio is in line with predictions from the thermal model, the $p/\pi$ ratio is found to be lower by a factor of about 1.5. This deviation from thermal model expectations is still to be understood.

• Received 14 August 2012

DOI:https://doi.org/10.1103/PhysRevLett.109.252301

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© 2012 CERN, for the ALICE Collaboration