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

Abstract The lifetime of the B s 0 meson is measured in approximately 3 million hadronic Z decays accumulated using the ALEPHdetector 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 B s 0 decays. Two hundred and eight D s − l + candidates satisfy selection criteria designed to ensure precise proper timereconstruction and yield a measured B s 0 lifetime of τ (B s 0 ) = 1.59 −0.15 +0.17 ( stat) ±0.03 (syst) ps. Using a larger, less constrained sample of events, the product branching ratio is measured to be Br ( b → B s 0 ) · Br(B s 0 → D s − l + νX) = 0.82 ± 0.09 ( stat) −0.14 +0.13 (syst) %.