Measurement of prompt D_s⁺-meson production and azimuthal anisotropy in Pb–Pb collisions at s_NN=5.02TeV

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⁺/D⁰ 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 v₂ 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⁺/D⁰ ratio, and v₂ 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.