A Preliminary Direct Measurement of the Parity - Violating Coupling of the Z 0 to Strange Quarks

We present an updated direct measurement of the parity-violating coupling of the Z 0 to strange quarks, A s , derived from the full SLD data sample of approximately 550,000 hadronic decays of Z 0 bosons produced with a polarized electron beam and recorded by the SLD experiment at SLAC between 1993 and 1998. Z 0 → s¯ s events are tagged by the presence in each event hemisphere of a high-momentum K ± , K s or Λ 0 / ¯ Λ 0 identified using the Cherenkov Ring Imaging Detector and/or a mass tag. The CCD vertex detector is used to suppress the background from heavy-flavor events. The strangeness of the tagged particle is used to sign the event thrust axis in the direction of the initial s quark. The coupling A s is obtained directly from a measurement of the left-right-forward-backward production asymmetry in polar angle of the tagged s quark. The background from u¯ u and d ¯ d events is measured from the data, as is the analyzing power of the method for s¯ s events. We measure: A s = 0.85 ± 0.06(stat.) ± 0.07(syst.)(preliminary).