A Preliminary Direct Measurement of the s-Quark Coupling

We present an updated direct measurement of the parity-violating coupling of the Z boson to strange quarks, A_s, derived from the full SLD data sample of approximately 550,000 hadronic decays of Z bosons produced with a polarized electron beam and recorded by the SLD experiment at SLAC between 1993 and 1998. Events with primary strange quarks are tagged by the presence in each event hemisphere of a high-momentum charged K meson, neutral K meson or Lambda hyperon 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 strange 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 strange quark. The background from primary up and down events is measured from the data, as is the analyzing power of the method for primary strange events. We measure: A_s = 0.85 +- 0.06(stat.) +- 0.07(syst.) (preliminary).