discovery of the W and Z
By the late 1970s the electroweak theory was a beautiful idea with a clear, daunting demand: somewhere out there had to be three heavy carrier particles, the W and Z bosons, weighing roughly 85 to 95 times as much as a proton. Producing such heavy objects required smashing particles together with far more energy than ever before. The discovery of the W and Z in 1983 was the moment that turned the electroweak theory from elegant mathematics into established physics.
The breakthrough came at CERN, where Carlo Rubbia and Simon van der Meer led an audacious plan to collide protons against antiprotons at very high energy. Van der Meer invented a clever technique to compress and focus the antiproton beam (called stochastic cooling) so that enough collisions would occur. Two large detectors, UA1 and UA2, watched for the telltale signatures: a W boson revealing itself as a single high-energy electron or muon flying out sideways with missing energy carried away by an unseen neutrino, and a Z boson appearing as a clean pair of opposite-charge leptons whose combined mass always added up to about 91 GeV.
The masses matched the electroweak predictions almost exactly, a stunning confirmation. Rubbia and van der Meer shared the Nobel Prize in 1984, remarkably fast recognition. The discovery cemented the Standard Model and demonstrated a powerful experimental strategy — hunt for a heavy particle by reconstructing the mass of the lighter particles it decays into. That same bump-hunting logic would later be used to find the top quark and the Higgs boson.
The Z boson revealed itself as a pair of leptons — say an electron and a positron — whose energies and momenta, added together, always reconstructed to the same mass near 91 GeV. Plotting that combined mass for many events produces a sharp peak: the unmistakable fingerprint of a new particle.
A sharp mass peak near 91 GeV announced the Z boson at CERN in 1983.
The 1983 experiments discovered the W and Z themselves; the Higgs boson, which explains why they are heavy, was not found until 2012 and is a separate story.