A Study of Bs Meson Oscillation Using Ds-Lepton Correlations
  From data collected around the Z resonance by the OPAL detector at LEP, a sample of Bs decays was obtained using Ds^-l^+ combinations, where the Ds^- was fully reconstructed in the phi pi-, K*0K- and Ks0K- decay channels or partially reconstructed in the phi l- nu (X) decay channel. These events were used to study Bs oscillation. The flavor (b or bbar) at decay was determined from the lepton charge while the flavor at production was determined from a combination of techniques. The expected sensitivity of the experiment is 4.1 ps-1. The experiment was not able to resolve the oscillatory behavior, and we deduced that the Bs oscillation frequency Delta m_s > 1.0 ps-1 at the 95% confidence level. 
The OPAL collaboration, G. Abbiendi, et al