Resonant structure and flavour tagging in the Bπ± system using fully reconstructed B decays

Starting from a sample of four million hadronic Z decays collected with the ALEPH detector at LEP, 404 charged and neutral B mesons are fully reconstructed and used to look for resonant structure in the Bπ system. An excess of events is observed above the expected background in the Bπ mass spectrum at a mass ≈5.7 GeV/c2, consistent with the production and decay to B(∗)π of the B∗∗ states predicted by Heavy Quark Symmetry (HQS). In the framework of HQS, it is found that the mass of the B2∗ state is (5739+ 8−11(stat)+6−4(syst)) MeV/c2 and the relative production rate of the B∗∗ system is BR(b→B∗∗→B(∗)π)/BR(b→Bu,d)=(31±9(stat)+6−5(syst))%. In the same sample of B mesons, significant Bπ± charge-flavour correlations are observed, which may prove important for tagging the initial B state in future CP violation studies.