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Summary of Weak Mixing Angle Measurements 
                   at CERN and SLAC     

Measurements of the Weak Mixing Angle by 4 LEP Experiments (combined) at CERN, and the SLD Experiment at SLAC.  The SLD result is shown in light blue and the other measurements are from CERN.  (The error bars shown for the measurements represent +/- 1 standard deviation.)  Leptonic results are determined from asymmetry measurements in the production of Z0 particles from polarized electron-positron collisions (SLD's Al measurement) and from LEP's asymmetry measurements in Z0 decays to pairs of leptons (electron pairs, muon pairs, and tau pairs) -- the Afb0,l and At and Ae measurements.  These leptonic results are consistent with each other.  Forward-backward asymmetry measurements in Z0 decays to pairs of quarks  can also be used to determine the weak mixing angle.   The quark asymmetry measurements are Afb0,b, Afb0,c and Qfb in the above plot, and they also are self-consistent.  But the leptonic results differ significantly (by 3.5 standard deviations) from the hadronic results.  The reason for this discrepancy could be a statistical fluctuation, an experimental technique problem, or perhaps a sign of new physics.


Last updated 04-09-2001