Measurement of prompt -meson production and azimuthal anisotropy in Pb–Pb collisions at

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 $\sqrt{{s}_{\mathrm{NN}}}=5.02\phantom{\rule{0.25em}{0ex}}\text{TeV}$ 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 ${D}_{s}^{+}\to \varphi {\pi }^{+}$, with $\varphi \to {K}^{-}{K}^{+}$, in the ${p}_{T}$ intervals $2<{p}_{T}<50\phantom{\rule{0.25em}{0ex}}\text{GeV}/c$ and $2<{p}_{T}<36\phantom{\rule{0.25em}{0ex}}\text{GeV}/c$ for the 0–10% and 30–50% centrality intervals. For ${p}_{T}>10\phantom{\rule{0.25em}{0ex}}\text{GeV}/c$, the measured ${D}_{s}^{+}$-meson nuclear modification factor ${R}_{\mathrm{AA}}$ is consistent with the one of non-strange D mesons within uncertainties, while at lower ${p}_{T}$ a hint for a ${D}_{s}^{+}$-meson ${R}_{\mathrm{AA}}$ 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 $2<{p}_{T}<8\phantom{\rule{0.25em}{0ex}}\text{GeV}/c$ 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 ${R}_{\mathrm{AA}}$, ${D}_{s}^{+}/{D}^{0}$ 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.