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

Abstract

The elliptic flow coefficient (v 2 ) of identified particles in Pb-Pb collisions at s 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 || > 0.9 between the identified hadron under study and the reference particles. The v 2 is reported for , K , K 0 S , p+p, , +, -+ + and -+ + 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 and the combined K and K 0 S 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 p+p, , + and -+ + . 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.