Measurement of Ds+meson production in Z decays and of the anti Bs0 lifetime

Ds+ mesons produced inZ0bb events were separated from theZ0cc component using a lifetime tag. Using a sample of 1.5 million hadronicZ decays collected with the Alephdetector theBs0 andDs+ yields have been measured:\begin{eqnarray*} B(b\to\bar B^0_s)B(\bar B^0_s\to D^+_s) & = & 0.088 \pm 0.020 \mathrm{(stat.)} \\ && \phantom{0.088} \pm 0.020 \mathrm{(syst.)} \\ B(c\to D^+_s) & = & 0.128 \pm 0.019 \mathrm{(stat.)}^ {+0.019}_{-0.016}\mathrm{(syst.)} \end{eqnarray*} The Bs0 lifetime was measured in aBs0 enriched sample reconstructing the decay length from the vertex of theDs+ with a hadron from theBs0 decay. The result obtained is: Bs=161+030−029(stat)+018−016(syst) ps