THE FORWARD-BACKWARD ASYMMETRY OF E(+) E(-) -] B(B)OVER-BAR AND E(+) E(-) -] C(C)OVER-BAR USING LEPTONS IN HADRONIC Z(0) DECAYS

The forward-backward asymmetries of e+e- --> Z0 --> bbBAR and e+e- --> Z0 --> ccBAR have been measured by the OPAL Collaboration using samples of hadronic Z0 decays in which electron or muon candidates were observed. The asymmetries were measured simultaneously in a two parameter fit, which used the distributions of the track momentum and transverse momentum component with respect to the associated jet to distinguish lepton candidates from different sources. From a sample of 360 000 hadronic events with centre-of-mass energies within +/- 0.5 GeV of the Z0 mass and mean energy 91.24 GeV, the values obtained for the bbBAR asymmetry before and after correcting for the effect of B0B0BAR mixing, and for the ccBAR asymmetry are, respectively: A(FB)b,mix = 0.070 +/- 0.014 (stat) +/- 0.005 (sys) , A(FB)b = 0.092 +/- 0.018 (stat) +/- 0.007 (sys) +/- 0.003 (mix), A(FB)c = 0.014 +/- 0.030 (stat) +/- 0.020 (sys). The measurement of the bbBAR asymmetry Is confirmed by a measurement using only leptons with high transverse momentum. This sample is highly enriched in semileptonic decays of b hadrons. Measurements using high transverse momentum leptons were also performed using samples of events with centre-of-mass energies further from the Z0 mass. After correcting for the effect of B0B0 mixing, the results are: A(FB)b ([square-root s] = 89.66 GeV) = 0.071 +/- 0.054 (stat) +/- 0.007 (sys) +/- 0.002 (mix), A(FB)b ([square-root s] = 92.75 GeV) = 0. 1 31 +/- 0.047 (stat) +/- 0.012 (sys) +/- 0.004 (mix).