2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/202355We report a measurement of the B^0_s meson lifetime from B_s^0 -> D^-_s X decays, where D_s^- mesons are reconstructed in the D_s^- -> phi pi^- and D_s^- -> K^{*0} K^- 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 meson decays. Fitting the distribution of the distance from the beam spot to the decay vertex of the D_s^- candidates with an unbinned likelihood function we measure tau(B_s^0) = 1.72 + 0.20 - 0.19 + 0.18 - 0.17 ps, where the errors are statistical and systematic, respectively.17 pages, LaTeX, uses a4p.sty, 3 eps figures included, submitted to Zeit. Phys. CHigh Energy Physics - Experimenttext