Measurement of Ab and Ac using a Lepton Tag at SLD  
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We present a direct measurement of the parity violation parameters 
Ab and Ac from the decay of polarized Z0 into b and c quarks. 
Ab and Ac are derived from the left-right forward-backward asymmetry of 
b and c quarks tagged via leptons from semileptonic decays. The lepton 
identification algorithm combines information from tracking, calorimetry 
and from the SLD Cherenkov Ring Imaging Detector. The values of Ab and 
Ac are extracted using a maximum likelihood fit to the differential 
cross section for fermion production. Vertexing information and decay 
kinematics have been used to discriminate among the different sources 
of tagged leptons. A new treatment of mixing effects and of background 
contamination has been introduced and a new vertexing algorithm has 
been used in the muon analysis. Based on the full 1993-1998 SLD data 
sample of 550K hadronic Z0 decays with highly polarized electron beams, 
we have measured Ab (Ac) with a ~3% (~5%) statistical error.