Measurement of the b forward-backward asymmetry and mixing using high-p⊥ leptons

The B0 - B0 average mixing parameter χ and b forward-backward asymmetry A0FB (b) are measured from a sample of about 4 200 000 Z -> qq events recorded with the ALEPH detector at LEP in the years 1990-1995. High transverse momentum electrons and muons produced in b semileptonic decays provide the tag of the quark flavour and of its charge. The average mixing parameter and the pole b asymmetry are measured to be χ = 0.1246 +/- 0.0051stat +/- 0.0052syst, A0FB (b) = 0.1008 +/- 0.0043stat +/- 0.0028syst. The value of sin2θeffW = 0.23198 +/- 0.00092 is extracted from the asymmetry measurement.