The ψ and ϒ resonances were startling and largely unanticipated. By contrast, it was apparent far in advance that the Z would be spectacular in e+e− annihilation. Indeed, within the Standard Model nearly every aspect of the Z could be predicted to the extent that sin2 θW was known. Despite this, the study of the Z in e+e− annihilation was a singular achievement in particle physics.

After initial planning as early as 1976, CERN began construction of the Large Electron Positron collider in 1983. Because ultrarelativistic electrons lose energy rapidly through synchrotron radiation, whose intensity varies as E4/ρ where ρ is the radius of curvature, LEP was designed with a large circumference, 26.67 km. The first collisions occurred on August 13, 1989.

In a daring move, SLAC aimed to reach the Z before LEP by colliding electron and positron beams generated with its linear accelerator. At the Stanford Linear Collider each bunch would be lost after colliding with the opposing bunch. While the Mark II detector, which had seen service at PEP, was refurbished, four new detectors – ALEPH, DELPHI, L3, and OPAL – were built at CERN.