Azimuthal anisotropy of D-meson production in Pb-Pb collisions at √sN N = 2.76 TeV

The production of the prompt charmed mesons D0, D+, and D∗+ relative to the reaction plane was measured in Pb-Pbcollisionsatacenter-of-massenergypernucleon-nucleoncollisionof√sNN =2.76TeVwiththeALICE detector at the CERN Large Hadron Collider. D mesons were reconstructed via their hadronic decays at central rapidity in the transverse-momentum (pT ) interval 2–16 GeV/c. The azimuthal anisotropy is quantified in terms of the second coefficient v2 in a Fourier expansion of the D-meson azimuthal distribution and in terms of the nuclear modification factor RAA, measured in the direction of the reaction plane and orthogonal to it. The v2 coefficient was measured with three different methods and in three centrality classes in the interval 0%–50%. A positive v2 is observed in midcentral collisions (30%–50% centrality class), with a mean value of 0.204+0.099 (tot. unc.) in the −0.036 interval 2 < pT < 6 GeV/c, which decreases towards more central collisions (10%–30% and 0%–10% classes). The positive v2 is also reflected in the nuclear modification factor, which shows a stronger suppression in the direction orthogonal to the reaction plane for midcentral collisions. The measurements are compared to theoretical calculations of charm-quark transport and energy loss in high-density strongly interacting matter at high tempera- ture. 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-pT yield of D mesons in central collisions and their azimuthal anisotropy in noncentral collisions.