A measurement of the $\mathrm{B_s^0}$ lifetime using reconstructed $\mathrm{ D_s^-}$ mesons

Abstract.

We report a measurement of the $\mathrm{B_s^0}$ meson lifetime from $\mathrm{B_s^0} \to \mathrm{ D_s^-} \rm{X}$ decays, where $\mathrm{ D_s^-}$ mesons are reconstructed in the $\mathrm{ D_s^-} \to \mathrm{\phi\pi^-}$ and $\mathrm{ D_s^-}\to\mathrm{K^{*0}K^-}$ decay channels. From approximately 3.7 million hadronic $\mathrm{Z}^0$ decays recorded by the OPAL detector at LEP a sample is selected containing 911 $\pm$ 83 candidates, of which $519 \pm 136$ are estimated to be from $\mathrm{B_s^0}$ meson decays. Fitting the distribution of the distance from the beam spot to the decay vertex of the $\mathrm{ D_s^-}$ candidates with an unbinned likelihood function we measure \[ \tau ({\rm B^0_{\rm s}} = 1.72^{+0.20+0.18}_{-0.19-0.17}\,{\rm ps}\; , \] where the errors are statistical and systematic, respectively.