CERN

byname of Organisation Europene pour la Recherche Nuclaire, formerly (195254) Conseil Europen pour la Recherche Nuclaire, English European Organization for Nuclear Research, international scientific organization established for the purpose of collaborative research into subnuclear physics (also called high-energy, or particle, physics). The organization operates expressly for research of a pure scientific and fundamental character, and the results of its experimental and theoretical work are made generally available. Headquarters are in Geneva, Switz. The establishment of CERN was at least in part an effort to reclaim the European physicists who had emigrated for various reasons to the United States as a result of World War II. The provisional organization, which was known as the Conseil Europen pour la Recherche Nuclaire (CERN), was proposed by the physicist Isidor Isaac Rabi at the fifth General Conference of UNESCO. Upon its actual establishment, the word Organisation replaced Conseil, although the organization continued to be known by the acronym of the earlier name. In the late 20th century it had a membership of 14 European nations, in addition to several nations that maintained observer status. CERN has the most powerful and versatile facilities of its kind in the world. The site covers more than 100 hectares (250 acres) in Switzerland and, since 1965, more than 450 hectares (1,125 acres) in France. The activation of a 600-megavolt synchrocyclotron in 1957 enabled CERN physicists to observe (some 22 years after the prediction of this activity) the decay of a pi-meson, or pion, into an electron and a neutrino. The event was instrumental in the development of the theory of weak interaction. The laboratory grew steadily, activating the particle accelerator known as the Proton Synchrotron (1959), which used strong focusing of particle beams; the Intersecting Storage Rings (ISR; 1971), enabling head-on collisions between protons; and the Super Proton Synchrotron (SPS; 1976), with a 7-kilometre (4.35-mile) circumference. With the addition of an Antiproton Accumulator Ring, the SPS was converted into a proton-antiproton collider in 1981 and provided experimenters with the discovery of the W and Z particles (carriers of the weak nuclear force) in 1983 by Carlo Rubbia and Simon van der Meer. The Large Electron-Positron Collider (LEP; 1989), which has a circumference of almost 27 km (17 miles), has facilitated detailed studies of the Z particle and the standard model of particle physics.