Determination of $\sin^2\theta^{\rm eff}_{\rm w}$ using jet charge measurements in hadronic Z decays

The electroweak mixing angle is determined with high precision from measurements of the mean difference between forward and backward hemisphere charges in hadronic decays of the Z. A data sample of 2.5 million hadronic Z decays recorded over the period 1990 to 1994 in the ALEPH detector at LEP is used. The mean charge separation between event hemispheres containing the original quark and antiquark is measured for b (b) over bar and c (c) over bar events in subsamples selected by their long lifetimes or using fast D*'s. The corresponding average charge separation for light quarks is measured in an inclusive sample from the anticorrelation between charges of opposite hemispheres and agrees with predictions of hadronisation models with a precision of 2%. It is shown that differences between light quark charge separations and the measured average can be determined using hadronisation models, with systematic uncertainties con strained by measurements of inclusive production of kaons, protons and Lambda's. The separations are used to measure the electroweak mixing angle precisely as sin^2( theta(w)(eff)) = 0.2322 +/- 0.0008(exp. stat.) +/-0.0007(exp. syst.) +/- 0.0008(sep.). The first two errors are due to purely experimental sources whereas the third stems from uncertainties in the quark charge separations