Observation of exclusive decays of B mesons at LEP

Data collected with the OPAL detector at LEP during 1990–1992 are used to study exclusive decays of B mesons. We observe the decay Bd0 → D∗−π+ and several Bs0 candidates in the modes Bs0 → J/ψφ and Bs0 → Ds−π+. Using one unambiguous event in the mode Bs0 → J/ψφ, we measure the mass of the Bs0 meson to be 5.359 ± 0.019 ± 0.007 GeV/c2.