The production of prompt D+s mesons was measured for the first time in collisions of heavy nuclei with the ALICE detector at the LHC. The analysis was performed on a data sample of Pb-Pb collisions at a centre-of-mass energy per nucleon pair, √sNN of 2.76 TeV in two different centrality classes, namely 0–10% and 20–50%. D+s mesons and their antiparticles were reconstructed at mid-rapidity from their hadronic decay channel D+s → φπ+, with φ → K−K+, in the transverse momentum intervals 4 < pT < 12 GeV/c and 6 < pT < 12GeV/c for the 0–10% and 20–50% centrality classes, respectively. The nuclear modification factor RAA was computed by comparing the pT-differential production yields in Pb-Pb collisions to those in proton-proton (pp) collisions at the same energy. This pp reference was obtained using the cross section measured at √s = 2.76 TeV. The RAA of D+s mesons was compared to that of non-strange D mesons in the 10% most central Pb-Pb collisions. At high pT (8 < pT < 12 GeV/c ) a suppression of the D+s -meson yield by a factor of about three, compatible within uncertainties with that of non-strange D mesons, is observed. At lower pT (4 < pT < 8 GeV/c ) the values of the D+s -meson RAA are larger than those of non-strange D mesons, although compatible within uncertainties. The production ratios D+s /D0 and D+s /D+ were also measured in Pb-Pb collisions and compared to their values in proton-proton collisions.
