Elliptic flow of identified hadrons in Pb-Pb collisions at \( \sqrt{s_{\mathrm{NN}}}=2.76 \) TeV

Abstract

The elliptic flow coefficient (v 2) of identified particles in Pb-Pb collisions at \( \sqrt{s_{\mathrm{NN}}}=2.76 \) TeV was measured with the ALICE detector at the Large Hadron Collider (LHC). The results were obtained with the Scalar Product method, a two-particle correlation technique, using a pseudo-rapidity gap of |Δη| > 0.9 between the identified hadron under study and the reference particles. The v 2 is reported for π ±, K±, K 0S , \( \mathrm{p}+\overline{\mathrm{p}} \), ϕ, \( \Lambda +\overline{\Lambda} \), \( {\Xi}^{-}+{\overline{\Xi}}^{+} \) and \( {\Omega}^{-}+{\overline{\Omega}}^{+} \) in several collision centralities. In the low transverse momentum (p T) region, p T < 3 GeV/c, v 2(p T) exhibits a particle mass dependence consistent with elliptic flow accompanied by the transverse radial expansion of the system with a common velocity field. The experimental data for π ± and the combined K± and K 0S results, are described fairly well by hydrodynamic calculations coupled to a hadronic cascade model (VISHNU) for central collisions. However, the same calculations fail to reproduce the v 2(p T) for \( \mathrm{p}+\overline{\mathrm{p}} \), ϕ, \( \Lambda +\overline{\Lambda} \) and \( {\Xi}^{-}+{\overline{\Xi}}^{+} \). For transverse momentum values larger than about 3 GeV/c, particles tend to group according to their type, i.e. mesons and baryons. The present measurements exhibit deviations from the number of constituent quark (NCQ) scaling at the level of ±20% for p T > 3 GeV/c.

A preprint version of the article is available at ArXiv.

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