Direct Measurement of Parity Violation in the Coupling of ${\mathit{Z}}^0$ Bosons to $\mathit{b}$ Quarks 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 $A_b=0.911\mathrm{}\pm 0.045\left(\mathrm{stat}\right)\pm 0.045\left(\mathrm{syst}\right)$.