Investigation of the Decay of Orbitally-Excited B Mesons and First Measurement of the Branching Ratio BR ( B ∗ J → B ∗ π ( X ) ) The OPAL Collaboration

From about 4 million hadronic Z0 decays recorded by the OPAL detector on and near to the Z0 resonance, we select a sample of more than 570 000 inclusively reconstructed B mesons. Orbitally-excited mesons B∗J are reconstructed using Bπ ± combinations. Independently, B mesons are reconstructed using the decay B → Bγ. The selected B candidates are used to obtain samples enriched or depleted in the decay B∗J → B π(X), where (X) refers to decay modes with or without additional accompanying decay particles. From the number of signal candidates in the Bπ mass spectra of these two samples, we perform the first measurement of the branching ratio of orbitally-excited B mesons decaying into Bπ(X): BR(B∗J → B π(X)) = 0.85 −0.27 ± 0.12 , where the first error is statistical and the second systematic. If B∗J decay modes other than single pion transitions can be neglected the measured ratio corresponds to the branching ratio BR(B∗J → B π). In the framework of Heavy Quark Symmetry, a simultaneous fit to the Bπ mass spectra of the samples enriched or depleted in B∗J → B π(X) decays yields the mass and the width of the B1(3/2) state, as well as the branching ratio of B ∗ J mesons decaying into Bπ: M(B1(3/2)) = ( 5.738 + 0.005 − 0.006 ± 0.007 ) GeV/c 2 Γ(B1(3/2)) = ( 18 + 15 + 29 − 13 − 23 ) MeV/c 2 BR(B∗J → B π) = 0.74 + 0.12 + 0.21 − 0.10 − 0.15 , where the uncertainties are statistical and systematic, respectively. (Submitted to Eur. Phys. J.)