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

TL;DR

This paper measures the elliptic flow of electrons from heavy-flavour hadron decays in Pb-Pb collisions at 2.76 TeV, revealing positive flow signals that suggest strong interactions of heavy quarks with the quark-gluon plasma.

Contribution

First measurement of heavy-flavour electron elliptic flow at mid-rapidity in Pb-Pb collisions at LHC energies, providing new insights into heavy quark-medium interactions.

Findings

Positive v2 observed across all centralities.

v2 decreases in more central collisions at low/intermediate pT.

Results align with models including elastic heavy quark interactions.

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 ($v_{\rm 2}$) represents the elliptic flow. The $v_{\rm 2}$ 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 $v_{\rm 2}$ 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 semi-central collisions (20-40%). The value of $v_{\rm 2}$ decreases towards more central collisions at low and intermediate $p_{\rm T}$ (0.5 $<$ $p_{\rm T}$ $<$ 3 GeV/$c$). The $v_{\rm 2}$ 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.