Measurement of Z<SUP>0</SUP> → bb̅ decays and the semileptonic branching ratio BR(b → ℓ + X)

We have measured the decay properties of Z0 → bb̅ 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 γbb = 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 λbb. The partial decay width of the Z0 into bb̅ has been measured to λ be λbb = 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 Z0 → bb̅ events has been determined to be ℓxEℓ = 0.686 ± 0.006 (stat.) ± 0.016 (syst.)