"Science progresses in two ways," says Herwig Schopper, who was director general of CERN between 1980 and 1988. "There are great discoveries, sometimes unexpected, that make headlines, and there is also steady tedious work that, after a length of time, gives a completely new picture of the world. Feynman compared it to looking at the clouds: there is no change when you look, but when you look again 15 minutes later it is completely different! Unfortunately this second class of discovery - which is extremely important - does not make headlines." This list of highlights from the first 50 years of CERN inevitably favours discoveries of the first type.
Pion decay: observed at CERN’s first accelerator, the synchro-cyclotron, in 1958, the decay of a pion into an electron was CERN’s first major physics discovery and an important development in our understanding of the weak force.
Neutrino horn: in 1961 accelerator expert Simon van der Meer discovered a way to make intense beams of neutrinos. The technique is still widely used in neutrino experiments today.
Aces: in an internal CERN report in January 1964, George Zweig published his theory about nucleons being made of smaller particles called aces. Unfortunately for him, Murray Gell-Mann had a similar idea at about the same time and we now call these particles quarks instead.
Multiwire proportional chamber: developed by Georges Charpak in 1968, this new approach to detecting charged particles increased the data-collection speed by a factor of 1000 compared with previous techniques, and was recognized with CERN’s second Nobel prize in 1992.
Strings: originally proposed by Gabriele Veneziano in 1968 as a model of the strong force, strings – and later superstrings – have dominated searches for a unified theory of the fundamental forces for the past 20 years.
Proton-proton collisions: first achieved at the Intersecting Storage Rings (ISR) in 1971, six months ahead of the rival AGS machine at Brookhaven. However, the ISR lost out to its US rival, which went on to discover the charm quark in the J/ψ meson.
Weak neutral currents: discovered by the Gargamelle detector in 1973, this result clinched the 1979 Nobel prize for Sheldon Glashow, Abdus Salam and Steven Weinberg by confirming a key prediction of the electroweak theory, although it was never recognized with a Nobel prize of its own.
Supersymmetry: in 1973 Bruno Zumino and Julius Wess proposed a new form of symmetry between fermions and bosons that is still the preferred option for physics beyond the Standard Model. Searching for evidence of supersymmetry is one of the top priorities for the LHC.
Stochastic cooling: this technique, developed by Simon van der Meer in 1978, was crucial in achieving an antiproton beam of high enough quality to discover the W and Z bosons in proton-antiproton collisions at the Super Proton Synchrotron five years later.
W and Z bosons: discovered by the UA1 and UA2 experiments in 1983, again confirming the predictions of the electroweak theory, the W and the Z brought CERN its first Nobel prize in 1984. The prize was shared by Carlo Rubbia, leader of UA1, and van der Meer.
LEP: it is difficult to do justice in a few words to the achievements of the Large Electron Positron (LEP) collider, which ran from 1989 to 2000. Data from LEP proved that there are only three generations of neutrinos, and its precision measurements of electroweak and strong physics greatly increased faith in the Standard Model of particle physics. LEP almost certainly played a role in the award of the 1999 Nobel prize to Gerard ‘t Hooft and Martinus Veltman for their theoretical work on electroweak interactions. At the end of its life, LEP revealed tantalizing hints of the Higgs boson.
The Web: in 1990 Tim Berners-Lee, a British physics graduate, and Robert Cailliau, a Belgian computer scientist, developed a way to link related pieces of information stored on different computers. The Web took off in the mid-1990s and the world was never the same again.
Anti-atoms: antihydrogen was created for the first time at the Low Energy Antiproton Ring (LEAR) in 1995. Although only nine anti-atoms were created in this experiment, by 2002 teams using the Antiproton Decelerator were able to trap hundreds of thousands of antihydrogen atoms.
