W and Z bosons
Around 1968 Sheldon Glashow, Steven Weinberg, and Abdus Salam came up with the electroweak theory, which unified electromagnetism and weak interactions, and for which they shared the 1979 Nobel Prize in Physics. The theory postulated the existence of W and Z bosons, and the pressure on the research community to prove the existence of these particles experimentally was substantial. During the 70s it was established that the masses of the W and Z bosons were in the range of 60 to 80 GeV (W boson) and 75 to 92 GeV (Z boson) — energies too large to be accessible by any accelerator in operation at that time. In 1976, Carlo Rubbia, Peter McIntyre and David Cline proposed to modify a proton accelerator — at that time a proton accelerator was already running at Fermilab and one was under construction at CERN (SPS) — into a proton–antiproton collider, able to reach energies large enough to produce W and Z bosons. The proposal was adopted at CERN in 1978, and the Super Proton Synchrotron (SPS) was modified to occasionally operate as a proton-antiproton collider (SpS).