A measurement of the B(s)(0) lifetime using reconstructed D(s)(-) mesons

We report a measurement of the B-s(0) mesonlifetime from B-s(0) --> Ds-X decays, where D-s(-) mesonsare reconstructed in the D-s(-) --> phi pi(-) and D-s(-) --> K*K-0(-) decay channels. From approximately 3.7 million hadronic Z(0) decays recorded by the OPAL detector at LEP a sample is selected containing 911 +/- 83 candidates, of which 519 +/- 136 are estimated to be from B-s(0) mesondecays. Fitting the distribution of the distance from the beam spot to the decay vertex of the D-s(-) candidates with an unbinned likelihood functionwe measuretau(B-s(0)) = 1.72(-0.19-0.17)(+0.20+0.18) ps,where the errors are statistical and systematic, respectively.