Primary authors: Francesco Noferini, Carlos Perez, You Zhou, Zhong-Bao Yin, Alexandru Florin Dobrin, Andrea Dubla, Redmer Bertens, Ajay Kumar Dash, Ionut Arsene, Mikolaj Krzewicki, Sergei Voloshin, Raimond Snellings, Ilya Selyuzhenkov, Paul Kuijer, P.C.

Abstract:

The $v_2$ of identified particles in Pb--Pb collisions at $\sqrt{\mathrm{s_{NN}}} = 2.76$~TeV was measured with the ALICE detector at the LHC. The results were obtained with the Scalar Product method, a two-particle correlation technique, using a pseudo-rapidity gap of $|\Delta\eta| > 0.9$ between the identified hadron under study and the reference particles. The $v_2$ is reported for $\pi^{\pm}$, $\mathrm{K}^{\pm}$, $\mathrm{K}^0_\mathrm{S}$, p+$\overline{\mathrm{p}}$, $\mathrm{\phi}$, $\Lambda$+$\overline{\mathrm{\Lambda}}$, $\Xi^-$+$\overline{\Xi}^+$ and $\Omega^-$+$\overline{\Omega}^+$ for several collision centralities. In the low transverse momentum ($p_{\rm T}$) region, $p_{\rm T} <2$~\gevc, $v_2(p_\mathrm{T})$ 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 $\pi^{\pm}$ and $\mathrm{K}$ are described fairly well by hydrodynamical calculations coupled to a hadronic cascade model (VISHNU). However, the same calculations fail to reproduce the $v_2(p_\mathrm{T})$ for p+$\overline{\mathrm{p}}$, $\mathrm{\phi}$, $\Lambda$+$\overline{\mathrm{\Lambda}}$ 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. However, the experimental data at the LHC exhibit deviations from the number of constituent quark (NCQ) scaling at the level of $\pm$20$\%$ for $p_{\mathrm{T}} > 3$~GeV/$c$.

Final results in PF: https://indico.cern.ch/event/306364/contribution/3/material/slides/0.pdf