, Volume 16, Issue 4, pp 555-578

Measurement of the \({\mathrm{B^0_s}}\) lifetime and study of \({\mathrm{B^0_s}}\) - \({\overline{\mathrm{B^0_s}}}\) oscillations using \({{\mathrm{ D_s}}\ell}\) events

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Lifetime and oscillations of \({\rm B^0_s}\) mesons have been studied in events with a large transverse momentum lepton and a \({\rm D_s}\) of opposite electric charge in the same hemisphere, selected from about 3.6 million hadronic \({\rm Z^0}\) decays accumulated by DELPHI between 1992 and 1995. The \({\rm B^0_s}\) lifetime and the fractional width difference between the two physical \({\rm B^0_s}\) states have been found to be:

\[ \tau_{{\rm B^0_s}} = (1.42^{+0.14}_{-0.13}(stat.)\pm 0.03(syst.)) ps \] \[ \Delta \Gamma_{\rm B^0_s}/\Gamma_{\rm B^0_s} < 0.46 \mbox{at the 95\% C.L.} \]

In the latter result it has been assumed that \(\tau_{{\rm B^0_s}}=\tau_{\rm B_d^}\) . Using the same sample, a limit on the mass difference between the physical \(\mbox{B}^0_{\mathrm s}\) states has been set:

\begin{eqnarray*} \begin{array}{ll} \Delta m_{\rm B^0_s} > 7.4 \mbox{ps}^{-1} \mbox{at the 95\% C.L.} & \end{array} \end{eqnarray*}

with a corresponding sensitivity equal to \(8.1 ps^{-1}\) .

Received: 7 February 2000 / Revised version: 23 March 2000 / Published online: 8 June 2000