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.
Highlights
(|y| < 0.7) is measured in Pb–Pb collisions at sNN = 2.76 TeV with ALICE at the LHC
A decreasing trend of v2e±←−HF towards central collisions is observed. This is consistent with a final-state anisotropy in momentum space driven by the initial geometrical anisotropy of the nucleons participating in the collision, which increases towards peripheral collisions. This result indicates that the interactions with the medium constituents transfer to heavy quarks, mainly charm, information on the azimuthal anisotropy of the system, possibly suggesting that charm quarks participate in the collective expansion of the system
We presented the elliptic flow of electrons from heavy-flavour hadron decays at mid-rapidity √
Summary
The ALICE experimental apparatus is described in detail in [1, 52]. The global reference system has the z-axis parallel to the beam line, the x-axis pointing towards the centre of the LHC accelerator ring and the y-axis pointing upward. At a radial distance of 3.7 m from the beam axis, the TOF detector [55] improves further the particle identification capability of ALICE. It provides a measurement of the time of flight for the particles from the interaction point up to the detector itself with an overall resolution of about 80 ps for pions and kaons at pT = 1 GeV/c in the Pb–Pb collision centrality intervals used in this analysis. Events with a reconstructed interaction vertex (primary vertex), determined by extrapolating charged-particle tracks to the beam line, with |z| < 10 cm from the nominal interaction point are used in the analysis in order to minimize edge effects at the limit of the central barrel acceptance. The EMCal trigger is not used in the 0–10% centrality class because of the high statistics achieved with the central trigger
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