Direct Measurement of Ab using Charged Kaons at the SLD Detector

We report a new measurement of Ab using data obtained by SLD in 1997-98. This measurement uses a vertex tag technique, where the selection of a b hemisphere is based on the reconstructed mass of the bottom hadron decay vertex. The method uses the 3D vertexing capabilities of SLD's CCD vertex detector and the small and stable SLC beams to obtain a high b-event tagging efficiency and purity of 78% and 97%, respectively. Charged kaons identified by the CRID detector provide an efficient quark-antiquark tag, with the analyzing power calibrated from the data. We obtain a preliminary result of Ab = 0.997 ± 0.044 ± 0.067