Measurement of the polarized forward-backward asymmetry of Z{sup 0} {yields} b{bar b} using a lifetime tag and momentum-weighted track charge

We present a direct measurement of the parity-violating parameter A{sub b} by analyzing the left-right forward-backward asymmetry of b quarks in e{sup +}e{sup {minus}} {yields} Z{sup o} {yields} b{bar b}. The SLD experiment observes hadronic decays of Z{sup o} bosons produced at resonance in collisions of longitudinally polarized electrons and unpolarized positrons at the SLC. Heavy flavor decays of the Z{sup o} are identified by taking advantage of the long lifetime of B hadrons, the small, stable SLC beam spot, and precise tracking from SLD. The asymmetry A{sub b} is measured with a self-calibrating technique employing momentum-weighted track charge from both hemispheres in the tagged events. From our 1994--1995 sample of 3.6 pb{sup {minus}1} of e{sup +}e{sup {minus}} annihilation data with a luminosity-weighted average e{sup {minus}} polarization of 77.3%, and our 1993 sample of 1.8 pb{sup {minus}1} with a luminosity-weighted polarization of 63.1%, we obtain A{sub b}(preliminary) = 0.843 {plus_minus} 0.046(stat.) {plus_minus} 0.051(syst.)