A measurement of the forward-backward asymmetries of e+e - → bb̄ and e+e- → cc̄ events using electrons and muons produced in semileptonic decays of bottom and charm hadrons is presented. The outputs of two neural networks designed to identify b → ℓ- and c → ℓ+ decays are used in a maximum likelihood fit to a sample of events containing one or two identified leptons. The b and c quark forward-backward asymmetries at three centre-of-mass energies √s and the average B mixing parameter χ are determined simultaneously in the fit. Using all data collected by OPAL near the Z resonance, the asymmetries are measured to be: AFB bb̄ = (4.7 ± 1.8 ± 0.1)%, AFB cc̄ = (-6.8 ± 0.9)% at 〈√s〉 = 89.51 GeV, AFBbb̄ = (9.72 ± 0.42 ± 0.15)%, A FBcc̄ = (5.68 ± 0.54 ± 0.39)% at 〈√s〉 = 91.25 GeV, AFBbb̄ = (10.3 ± 1.5 ± 0.2)%, AFBcc̄ = (14.6 ± 2.0 ± 0.8)% at 〈√s〉 = 92.95 GeV. For the average B mixing parameter, a value of: χ = (13.12 ± 0.49 ± 0.42)% is obtained. In each case the first uncertainty is statistical and the second systematic. These results are combined with other OPAL measurements of the b and c forward-backward asymmetries, and used to derive a value for the effective electroweak mixing angle for leptons sin2θ effℓ of 0.23238 ± 0.00052.
|Number of pages||19|
|Journal||Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics|
|State||Published - 18 Dec 2003|