Measurement of prompt Ds+-meson production and azimuthal anisotropy in Pb–Pb collisions at √sNN = 5.02 TeV

The production yield and angular anisotropy of prompt D _s ⁺ mesons were measured as a function of transverse momentum (p _T) in Pb–Pb collisions at a centre-of-mass energy per nucleon pair s _NN=5.02TeV collected with the ALICE detector at the LHC. D _s ⁺ mesons and their charge conjugates were reconstructed at midrapidity (|y|<0.5) from their hadronic decay channel D _s ⁺→ϕπ ⁺, with ϕ→K ⁻K ⁺, in the p _T intervals 2<p _T<50GeV/c and 2<p _T<36GeV/c for the 0–10% and 30–50% centrality intervals. For p _T>10GeV/c, the measured D _s ⁺-meson nuclear modification factor R _AA is consistent with the one of non-strange D mesons within uncertainties, while at lower p _T a hint for a D _s ⁺-meson R _AA larger than that of non-strange D mesons is seen. The enhanced production of D _s ⁺ relative to non-strange D mesons is also studied by comparing the p _T-dependent D _s ⁺/D ⁰ production yield ratios in Pb–Pb and in pp collisions. The ratio measured in Pb–Pb collisions is found to be on average higher than that in pp collisions in the interval 2<p _T<8GeV/c with a significance of 2.3σ and 2.4σ for the 0–10% and 30–50% centrality intervals. The azimuthal anisotropy coefficient v ₂ of prompt D _s ⁺ mesons was measured in Pb–Pb collisions in the 30–50% centrality interval and is found to be compatible with that of non-strange D mesons. The main features of the measured R _AA, D _s ⁺/D ⁰ ratio, and v ₂ as a function of p _T are described by theoretical calculations of charm-quark transport in a hydrodynamically expanding quark–gluon plasma including hadronisation via charm-quark recombination with light quarks from the medium. The p _T-integrated production yield of D _s ⁺ mesons is compatible with the prediction of the statistical hadronisation model.