Measurements of$B^0 - \bar B^0$ mixing,${{\Gamma (Z^0 \to b\bar b)} \mathord{\left/ {\vphantom {{\Gamma (Z^0 \to b\bar b)} {\Gamma (Z^0 \to hadrons)}}} \right. \kern-\nulldelimiterspace} {\Gamma (Z^0 \to hadrons)}}$ and semileptonic branching ratios forb-flavoured hadrons in hadronicZ ⁰ decays

Abstract

From a sample of about 450 000 hadronicZ ⁰ decays, measurements of the average$B^0 - \bar B^0$ mixing parameter, χ, the branching fraction ofZ ⁰ bosons into hadrons containing bottom quarks,${{\Gamma (Z^0 \to b\bar b)} \mathord{\left/ {\vphantom {{\Gamma (Z^0 \to b\bar b)} {\Gamma (Z^0 \to hadrons)}}} \right. \kern-\nulldelimiterspace} {\Gamma (Z^0 \to hadrons)}}$, the average semileptonic branching ratios for such hadrons,B(b→l) andB(b→c→l), and the mean scaled energy of these hadrons, 〈x_E〉, are presented. The measurements were obtained using a simultaneous fit to single-lepton and dilepton events collected with the OPAL detector at LEP, including both electrons and muons. The results are

where the errors are statistical and systematic, respectively, in each case. The result forB)b→c→l) excludes decays of the typeb→→ℓ.