Precise measurement of the left-right cross section asymmetry in Z boson production by E+e- collisions

The authors present a precise 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 91.26 GeV with the SLD detector at the SLAC Linear Collider (SLC). The luminosity-weighted average polarization of the SLC electron beam was (63.0 ± 1.1)%. Using a sample of 49,392 Z decays, they measure ALR to be 0.1628 ± 0.0071 (stat.) ± 0.0028(syst.) which determines the effective weak mixing angle to be sin2 θWeff = 0.2292 ± 0.0009(stat.) ± 0.0004(syst.). They combine this result with the result obtained in 1992 and obtain sin2 θWeff = 0.2294 ± 0.0010, which constitutes the best measurement of sin2 θWeff in a single experiment presently available