Measurements of Z0 --> bb decays and the semileptonic branching ratio BR (b --> l + X)

Abstract We have measured the decay properties of Z 0 → b b from a study of inclusive muon and electron events. The average (e and μ) b-quark semileptonic branching ratio has been determined to be BR (b → l + X) = 0.119 ± 0.003 (stat.) ± 0.006 (syst.), assuming the standard model prediction of Γ bb = 378 ± 3 MeV. From the ratio of the number of dilepton events to single lepton events, we find BR (b → l + X) = 0.113 ± 0.010 (stat.) ± 0.006 (syst.), without assumptions on Λ bb . The partial decay width of the Z 0 into b b has been measured to be Λ bb = 385 ± 7 (stat.) ± 11 (syst.) MeV with an additional 19 MeV error from the uncertainty in BR (b → l + X). The average fractional energy of bottom hadrons in Z 0 → b b events has been determined to be 〈 x E 〉 = 0.686 ± 0.006 (stat.) ± 0.016 (syst.).