Investigation of the decay of orbitally-excited B mesons and first measurement of the branching ratio ${\rm BR}({\rm B}^*_J \rightarrow{\rm B}^* \pi (X))$

Abstract.

From about 4 million hadronic $\rm Z^0$ decays recorded by the OPAL detector on and near to the $\rm Z^0$ resonance, we select a sample of more than 570 000 inclusively reconstructed B mesons. Orbitally-excited mesons ${\rm B}^*_J$ are reconstructed using ${\rm B}\pi^\pm$ combinations. Independently, ${\rm B}^*$ mesons are reconstructed using the decay ${\rm B}^*\rightarrow{\rm B}{\gamma}$. The selected${\rm B}^*$ candidates are used to obtain samples enriched or depleted in the decay ${\rm B}^*_J \rightarrow{\rm B}^* \pi^{\pm}(X)$, where (X) refers to decay modes with or without additional accompanying decay particles. From the number of signal candidates in the ${\rm B}\pi^\pm$ mass spectra of these two samples, we perform the first measurement of the branching ratio of orbitally-excited B mesons decaying into ${\rm B}^*\pi(X)$:

${\rm BR}( {\rm B}^*_J \rightarrow{\rm B}^* \pi (X)) = 0.85^{ +0.26}_{ -0.27} \pm 0.12 ,$

where the first error is statistical and the second systematic.