Measurement of the Bs0 lifetime and production rate with Ds−l+ combinations in Z decays

The lifetime of the B0s meson is measured in approximately 3 million hadronic Z decays accumulated using the ALEPH detector at LEP from 1991 to 1994. Seven different D-s decay modes were reconstructed and combined with an opposite sign lepton as evidence of semileptonic B0s decays. Two hundred and eight D-sl+ candidates satisfy selection criteria designed to ensure precise proper time reconstruction and yield a measured B0s lifetime of τ(B0s) = 1.59 +0.17-0.15 (stat) +/- 0.03 (syst) ps. Using a larger, less constrained sample of events, the product branching ratio is measured to be Br(b -> B0s). Br(B0s -> D-sl+ νX) = 0.82 +/- 0.09 (stat) +0.13-0.14 (syst) %.