Measurement of $A_{\rm FB}^b$ using inclusive $b$-hadron decays

Abstract.

Based on a sample of four million events collected by ALEPH from 1991 to 1995, a measurement of the forward-backward asymmetry in $Z \rightarrow b\bar{b}$ decays using inclusive final states is presented. High-performance tagging of $b\bar{b}$ events in a wide angular range is achieved using neural network techniques. An optimal hemisphere charge estimator is built by merging primary and secondary vertex information, leading kaon identification and jet charge in a neural network. The average charge asymmetry, the flavour tagging efficiencies and mean b-hemisphere charges are measured from data and used to extract the pole b asymmetry in the Standard Model

\begin{eqnarray*} \nonumber A^{0,b}_{\rm FB} & = & 0.1011 \, \pm \,0.0027\,(stat) \,\pm \,0.0012\,(syst)\,, \end{eqnarray*}

corresponding to a value of the effective weak mixing angle of

\[ {\rm sin^2} \theta_{\rm W}^{\rm eff} = 0.23189 \pm 0.00056\,. \]