Elliptic flow of electrons from heavy-flavour hadron decays at mid-rapidity in Pb–Pb collisions at $\sqrt{s_{\rm NN}}= 2.76$ TeV

Abstract

The elliptic flow of electrons from heavy-flavour hadron decays at mid-rapidity ($|y| < 0.7$) is measured in Pb–Pb collisions at $\sqrt{s_{\rm NN}}= 2.76$ TeV with ALICE at the LHC. The particle azimuthal distribution with respect to the reaction plane can be parametrized with a Fourier expansion, where the second coefficient ($v_2$) represents the elliptic flow. The $v_2$ coefficient of inclusive electrons is measured in three centrality classes (0–10%, 10–20% and 20–40%) with the event plane and the scalar product methods in the transverse momentum ($p_{\rm T}$) intervals 0.5-13 GeV/$c$ and 0.5-8 GeV/$c$, respectively. After subtracting the background, mainly from photon conversions and Dalitz decays of neutral mesons, a positive $v_2$ of electrons from heavy-flavour hadron decays is observed in all centrality classes, with a maximum significance of $5.9\sigma$ in the interval $2 < p_{\rm T} < 2.5$ GeV/$c$ in semicentral collisions (20–40%). The value of $v_2$ decreases towards more central collisions at low and intermediate $p_{\rm T}$ ($0.5 < p_{\rm T} < 3$ GeV/$c$). The $v_2$ of electrons from heavy-flavour hadron decays at mid-rapidity is found to be similar to the one of muons from heavy-flavour hadron decays at forward rapidity ($2.5 < y < 4$). The results are described within uncertainties by model calculations including substantial elastic interactions of heavy quarks with an expanding strongly-interacting medium.