, Volume 18, Issue 2, pp 229-252

Study of \({\mathrm B^0_s}-\overline{\mathrm B^0_s}\) oscillations and \({\mathrm B^0_s}\) lifetimes using hadronic decays of \({\mathrm B^0_s}\) mesons

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Oscillations of \(\mbox{B}^0_{\mathrm{s}}\) mesons have been studied in samples selected from about 3.5 million hadronic \(\mathrm{Z}\) decays detected by DELPHI between 1992 and 1995. One analysis uses events in the exclusive decay channels: \(\mathrm{B^0_s}\rightarrow \rm{D}_{s}^{-} \pi^{+}\) or \(\rm{D}_{s}^{-}\mathrm{a_1^+}\) and \(\mathrm{B^0_s} \rightarrow \overline{\mathrm{D}}^0\mathrm{K}^-\pi^+ \) or \(\overline{\mathrm{D}}^0\mathrm{K}^-\mathrm{a_1^+}\) , where the \({\mathrm{D}}\) decays are completely reconstructed. In addition, \(\mbox{B}^0_{\mathrm{s}}-\overline{\mbox{B}^0_{\mathrm{s}}}\) oscillations have been studied in events with an exclusively reconstructed \({\mathrm{D_s}}\) accompanied in the same hemisphere by a high momentum hadron of opposite charge. Combining the two analyses, a limit on the mass difference between the physical \(\mbox{B}^0_{\mathrm{s}}\) states has been obtained:

\[ \Delta m_{\mathrm{B^0_s}} > 4.0 \mbox{ps}^{-1} \mbox{at the 95% C.L.}\]

\[ \mbox{with a sensitivity of} \Delta m_{\mathrm{B^0_s}} = 3.2 \mbox{ps}^{-1}.\]

Using the latter sample of events, the \(\mathrm{B^0_s}\) lifetime has been measured and an upper limit on the decay width difference between the two physical \(\mathrm{B^0_s}\) states has been obtained:

\[\tau_{\mathrm{B^0_s}} = 1.53^{+0.16}_{-0.15}(\rm{stat}.)\pm{0.07}(\rm{syst}.) \mathrm{ps}\]

\[\Delta \Gamma_{\mathrm{B^0_s}}/\Gamma_{\mathrm{B^0_s}} < 0.69 \mbox{at the 95% C.L.}\]

The combination of these results with those obtained using \({\rm{D}_{s}^{\pm}} \ell^{\mp}\) sample gives:

\[ \Delta m_{\mathrm{B^0_s}} > 4.9 \mbox{ps}^{-1} \mbox{at the 95% C.L.}\]

\[ \mbox{with a sensitivity of} \Delta m_{\mathrm{B^0_s}} = 8.7 \mbox{ps}^{-1}.\]

\[ \tau_{\mathrm{B^0_s}} = 1.46\pm{0.11} \mathrm{ps}\quad \mbox{and}\quad \Delta \Gamma_{\mathrm{B^0_s}}/\Gamma_{\mathrm{B^0_s}} < 0.45 \mbox{at the 95% C.L.} \]

Received: 5 July 2000 / Revised version: 25 September 2000 / Published online: 8 December 2000