$A_{FB}$ for $b\overline{b}$ and $c\overline{c}$

At LEP the forward-backward asymmetries in the distribution of the polar angle of charm (A/sub FB//sup c/) and bottom (A/sub FB//sup b/) quarks produced in the Z boson decay have been measured in about 4 million events collected by $9 each experiment. From the measurement of heavy flavour quark asymmetry a value of sin/sup 2/ theta /sub W, eff //sup l/ is determined with a relative accuracy of 1.6*10/sup -3/. (3 refs).