Improved Measurement of the Left-Right Z0 Cross Section Asymmetry

We present a new measurement of the left-right cross section asymmetry (ALR) for Z boson production by e+e- collisions. The measurement was performed at a center-of-mass energy of 91.28 GeV with the SLD detector at the SLAC Linear Collider (SLC). The luminosity-weighted average polarization of the SLC electron beam was (77.23±0.52)%. Using a sample of 93 644 Z decays, we measure the pole value of the asymmetry, ALR0, to be 0.1512±0.0042(stat)±0.0011(syst), which is equivalent to an effective weak mixing angle of sin 2 θWeff=0.231 00±0.000 54(stat)±0.000 14syst.