Review of experimental results on precision tests of electroweak theories

The current status of precision electroweak measurements, including data from LEP, the Fermilab Tevatron and the SLC, is reviewed. The data include measurements of the masses and widths of the W and Z bosons, as well as other data on Z-fermion couplings from measurements of cross sections, forward-backward asymmetries, $\tau$ polarisation and the left-right asymmetry $\ALR$. The data are used to test lepton universality. The results from LEP and the SLC on heavy quark couplings have also reached interesting levels of precision. The current, and still preliminary, data give world average values of the ratios of the quark partial to hadronic widths for b and c quarks, $\Rbb$ and $\Rcc$, which are about 3.7 and 2.5 standard deviations respectively from Standard Model (SM) fits to all electroweak data. Using these and other LEP and SLC data, the b and c quark-couplings are extracted. The global electroweak fits to all data give an indirect value of the top quark mass which is in good agreement with the direct measurement at the Tevatron by the CDF and D0 Collaborations; a significant triumph for the Standard Model. The influence of $\Rbb$ and $\Rcc$ on these fits is discussed. The global SM fits favour a light Higgs mass. However, the appropriate error scale for $\MH$ is logarithmic and the upper limits are sensitive to the inclusion of the data on $\Rbb$, $\Rcc$ and $\ALR$, all of which are somewhat discrepant from the SM expectations.