Search for B-s(0)-(B-s(0))over-bar oscillations in DELPHI using high-p(t) leptons

Oscillations in the $\mbox{B}^0_s$- $\overline{\mbox{B}^0_s}$ system were studied in events selected from about 4.3 million hadronic Z 0 decays registered by DELPHI between 1992 and 2000. This paper presents updates of two published analyses (11, 12). The first analysis, which utilizes leptons emitted with large momentum transverse to a jet, was improved by means of a better algorithm for the vertex reconstuction and a new algorithm for flavour-tagging at production time. The second analysis, which utilizes $\mbox{D}_s$-lepton events, was improved by optimizing the treatment of proper time resolution. No signal of $\mbox{B}^0_{\mathrm s}$ oscillations was observed and limits on the mass difference between the physical $\mbox{B}^0_{\mathrm s}$ states were obtained to be: \begin{displaymath}\Delta m_s> 8.0\,\mbox{ps}^{-1}~\mbox{at the 95\% C.L.} \end{displaymath} \begin{displaymath}\mbox{\rm {with a sensitivity of}}~~ \Delta m_s= 9.1\,\mbox{ps}^{-1}\end{displaymath} in the high pt lepton analysis and \begin{displaymath}\Delta m_s> 4.9\,\mbox{ps}^{-1}~\mbox{at the 95\% C.L.} \end{displaymath} \begin{displaymath}\mbox{\rm {with a sensitivity of}}~~ \Delta m_s= 8.6\,\mbox{ps}^{-1}\end{displaymath} in the $\mbox{D}_s$-lepton analysis. Previously published results on these analyses are superseded. The combination of these results with those obtained in other independent analyses previously performed in DELPHI ( $\mbox{D}_s$-hadron, exclusive $\mbox{B}^0_s$, inclusive vertex) gives: \begin{displaymath}\Delta m_s> 8.5\,\mbox{ps}^{-1}~\mbox{at the 95\% C.L.} \end{displaymath} \begin{displaymath}\mbox{\rm {with a sensitivity of}}~~ \Delta m_s= 12.0\,\mbox{ps}^{-1}.\end{displaymath}