An Improved Measurement of the Left-Right Z0 Cross Section Asymmetry

We present a new measurement of the left-right cross section asymmetry ( A LR ) 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, A 0 LR , to be 0.1512 ± 0.0042(stat.) ± 0.0011(syst.) which is equivalent to an effective weak mixing angle of sin 2 θ eff W = 0 . 23100 ± 0 . 00054(stat . ) ± 0 . 00014(syst . ).