Measurement of Ab from Left - Right Forward - BackwardAsymmetry

We present a direct measurement of the parity-violating parameter A b by analyzing the left-right forward-backward asymmetry of b quarks in polarized Z 0 decays with a nal state kaon charge tag. The 1994-1995 SLD data sample of 100,000 hadronic Z 0 decays produced with a highly polarized electron beam is used for this analysis. A b-enriched sample is obtained from a vertex-mass tag using a CCD-based vertex detector. The b quark charge is assigned on the basis of the charge of a kaon from the B decay cascade. The charged kaon is identiied by the Cerenkov Ring Imaging Detector. The parameter A b is extracted by forming a double asymmetry in polarization (left-right) and polar angle (forward-backward), with a preliminary result of A b = 0:891 0:083 stat 0:113 sys .