The parity-violating parameters $A_b$ and $A_c$ are directly measured by the SLD experiment at the SLAC Linear Collider in $e^{+}{e}^{-}$ collisions with polarized electrons at the $Z^0$ resonance. Leptons with distinctive total and transverse momenta are used to select and analyze $Z^0\to b\overline{b}$ and $Z^0\to c\overline{c}$ events. $A_b$ and $A_c$ are extracted by forming the left-right forward-backward asymmetry in electron beam polarization and quark polar angle. From our 1993 sample of 1.8 p${\mathrm{b}}^{–1}$ of $Z^0$ decay data with an average electron beam polarization of 63% we find $A_b=0.91\mathrm{}\pm 0.14$ (stat) $\pm 0.07$ (syst) and $A_c=0.37\mathrm{}\pm 0.23$ (stat) $\pm 0.21$ (syst).

• Received 4 October 1994

DOI:https://doi.org/10.1103/PhysRevLett.74.2895