The weak bosons W and Z

The observation in 1973, of neutrino interactions resulting in final states that did not contain any electron or muon, was the first experimental evidence in favour of a unified description of the weak and electromagnetic interactions. By determining the weak mixing angle, tentative predictions could be make for the mass values of the weak bosons, the W ± and Zsup (o) particles. Accelerators then available were inadequate to the task, but the more recently commissioned Stanford Linear Accelerator Collider and the large electron-positron ring at CERN will be more useful tools for observing the weak bosons Zsup (o) and W ±. The 450 GeV proton synchrotron (SPS) at CERN first observed the W → eυ decay in 1982, with Zo being observed a year later. A short description of this machine and major experiments performed on it is followed by the results of studies of weak boson properties. So far, experimental observations have been in good agreement with theoretical predictions based on the standard model of the unified electroweak theory. (UK)