Article révisé par les pairs
Résumé : From a sample of about 120 000 hadronic Z0 decays, using a technique based on a separation of the different event categories in the boosted sphericity product, the fraction of bb̄ decays has been measured to be 0.219 ± 0.014 (stat) ⋯ 0.019 (syst). Using the DELPHI determination of the hadronic Z0 width, this corresponds to a partial width Γbb- = 378 ± 42 MeV (in good agreement with the standard model prediction of ≃ 380 MeV). Combining this measurement with the determinations based on events with high pt leptons gives an estimate for the branching ratio of b into leptons at LEP of (11.2 ± 1.2)%, consistent with previous determinations.