Measurement of D_s⁺ production and nuclear modification factor in Pb-Pb collisions at √s_NN=2.76 TeV

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, √s_NN, 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 < p_T < 12GeV/c and 6 < p_T < 12 GeV/c for the 0–10% and 20–50% centrality classes, respectively. The nuclear modification factor R_AA was computed by comparing the p_T-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 = 7 TeV and scaled to √s = 2.76 TeV. The R_AA of D_s⁺ mesons was compared to that of non-strange D mesons in the 10% most central Pb-Pb collisions. At high p_T (8 < p_T < 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 p_T (4 < p_T < 8 GeV/c) the values of the D_s⁺-meson R_AA 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.