Azimuthal anisotropy of D meson production in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=2.76$ TeV

Abstract

The production of the prompt charmed mesons $D^0$, $D^{+}$ and $D^{\ast +}$ relative to the reaction plane was measured in Pb-Pb collisions at a centre-of-mass energy per nucleon-nucleon collision of $\sqrt{s_{\mathrm{NN}}}=2.76$ TeV with the ALICE detector at the LHC. D mesons were reconstructed via their hadronic decays at central rapidity in the transverse momentum ($p_{\mathrm{T}}$) interval of 2-16 GeV/$c$. The azimuthal anisotropy is quantified in terms of the second coefficient $v_2$ in a Fourier expansion of the D meson azimuthal distribution, and in terms of the nuclear modification factor $R_{\mathrm{AA}}$, measured in the direction of the reaction plane and orthogonal to it. The $v_2$ coefficient was measured with three different methods and in three centrality classes in the interval 0-50%. A positive $v_2$ is observed in mid-central collisions (30-50% centrality class), with an mean value of $0.204_{-0.036}^{+0.099}$ (tot.unc.) in the interval $2<p_{\mathrm{T}}<6$ GeV/$c$, which decreases towards more central collisions (10-30% and 0-10% classes). The positive $v_2$ is also reflected in the nuclear modification factor, which shows a stronger suppression in the direction orthogonal to the reaction plane for mid-central collisions. The measurements are compared to theoretical calculations of charm quark transport and energy loss in high-density strongly-interacting matter at high temperature. The models that include substantial elastic interactions with an expanding medium provide a good description of the observed anisotropy. However, they are challenged to simultaneously describe the strong suppression of high-$p_{\mathrm{T}}$ yield of D mesons in central collisions and their azimuthal anisotropy in non-central collisions.

36 pages, 11 captioned figures, 3 tables, published version, figures at http://aliceinfo.cern.ch/ArtSubmission/node/568

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