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, A0 LR, to be 0.1512 ± 0.0042(stat) ± 0.0011(syst), which is equivalent to an effective weak mixing angle of sin2θeff W=0.23100 ± 0.00054(stat) ± 0.00014(syst).
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