Direct Measurement of Parity Violation in the Coupling ofZ0Bosons tobQuarks Using a Mass Tag and Momentum-Weighted Track Charge

We present a direct measurement of the parity-violation parameter ${A}_{b}$ using a self-calibrating track-charge technique. In the SLAC Linear Collider Large Detector (SLD) experiment we observe hadronic decays of ${Z}^{0}$ bosons produced in collisions between longitudinally polarized electrons and unpolarized positrons at the SLAC Linear Collider. A sample of $b\overline{b}$ events is selected using the topologically reconstructed mass of $B$ hadrons. From our 1993--1995 sample of approximately 150 000 hadronic ${Z}^{0}$ decays, we obtain ${A}_{b}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0.911\ifmmode\pm\else\textpm\fi{}0.045(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.045(\mathrm{syst})$.