First measurement of the left-right Z cross section asymmetry in polarized e+e- collisions at the SLC

The SLAC Linear Collider (SLC) has recently been upgraded to produce, accelerate, and collide a spin polarized electron beam. The average beam polarization during the 1992 run was (22.4 ± 0.7)%. The SLD Collaboration used the polarized beam to perform the first 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 91.55 GeV with a sample of 10,224 Z decays. The measured value of ALR is 0.100 ± 0.044(stat.) ± O.004(syst.) which determines the effective weak mixing angle to be sin2θWeff = 0.2378 ± 0.0056(stat.) ± 0.0005(syst.)