Measurement of the BS0 lifetime

The lifetime of the Bs0 meson has been measured with the OPAL detector at LEP. A sample of Bs0 (B̄s0) decays has been obtained using Ds− l+ (and charge conjugate, where l denotes a lepton) combinations, where the Ds− was reconstructed in either the φπ− of K∗0K− channel. The decay lengths of Ds− l+ combinations were measured using vertex reconstruction. Proper decay times were obtained by combining these decay lengths with an estimate of the relativistic boost of the Bs0 and were used in a maximum likelihood fit for the mean Bs0 lifetime. From approximately 22 Ds− l+ combinations attributed to Bs0 decays (after background subtraction) in 1.26 million hadronic Z0 events recorded between 1990 and 1992, we have measured τBs = 1.13−0.26+0.35(stat) ± 0.09 (sys) ps.