Direct Measurement of $A_b$ and $A_c$ at the ${\mathit{Z}}^0$ Pole Using a Lepton Tag

The parity violation parameters $A_b$ and $A_c$ of the $\mathrm{Zb}\overline{b}$ and $\mathrm{Zc}\overline{c}$ couplings have been measured directly, using the polar angle dependence of the $Z^0$-pole polarized cross sections. Bottom and charmed hadrons were tagged via semileptonic decays. Both the muon and electron identification algorithms take advantage of new multivariate techniques, incorporating for the first time information from the SLD Čerenkov Ring Imaging Detector. Based on the 1993–1995 SLD sample of 150 000 $Z^0$ decays produced with highly polarized electron beams, we measure $A_b=0.910\mathrm{}\pm 0.068\left(\mathrm{stat}\right)\pm 0.037\left(\mathrm{syst}\right)$, $A_c=0.642\mathrm{}\pm 0.110\left(\mathrm{stat}\right)\pm 0.063\left(\mathrm{syst}\right)$.