FIRST MEASUREMENT OF THE LEFT-RIGHT ASYMMETRY IN Z-BOSON PRODUCTION

We present the first measurement of the left-right cross-section asymmetry (ALR) in Z-boson production observed at the SLAC Linear Collider. In 1992 the SLD detector recorded 10 224 Z events produced by the collision of longitudinally polarized electrons with an unpolarized positron beam at a center-of-mass energy of 91.55 GeV. The average electron beam polarization during the run was (22.4 ± 0.6)%. We measure ALR to be 0.100 ± 0.0440 (stat.) ±0.004 (syst.), which determines the effective weak mixing angle to be $\sin^2\theta_W^{\rm {eff}} = 0.2378\pm 0.0056\, ({\rm stat.})\pm 0.0005\, ({\rm syst.})$.