A measurement of AFBb in lifetime tagged heavy flavour Z decays

Abstract A new measurement of the forward-backward asymmetry in Z→ b b decays is presented. Hadrons from b decays are tagged using their long lifetimes. The b quark charge and direction are reconstructed with a hemisphere charge algorithm. The asymmetry and reconstructed b hemisphere charge are measured in the 69 pb −1 of data collected by ALEPH during 1991, 1992 and 1993. They are used to extract sin 2 θ W eff , which is determined to be 0.2315 ± 0.0016 (stat.) ± 0.0009 (syst.), corresponding to an A FB b of 0.0992 ± 0.0084 (stat.) ± 0.0046 (syst.).