CERN is the European Organization for Nuclear Research, the world's largest particle physics laboratory, situated on the border between France and Switzerland, just west of Geneva. It is the world's largest research centre for particle physics and the birthplace of the World Wide Web. The convention establishing it was signed on September 29, 1954. From the original 12 signatories of the CERN convention, membership has grown to the present 20 Member States.
Its main function is to provide the particle accelerators needed for high energy physics research and numerous experiments have been constructed at CERN by international collaborations to make use of them. The main site at Meyrin also has a large computer centre containing very powerful data processing facilities primarily for experimental data analysis, and because of the need to make them available to researchers elsewhere, has historically been (and continues to be) a major wide area networking hub.
CERN currently employs just under 3000 people full-time. Some 6500 scientists and engineers (representing 500 universities and 80 nationalities), about half of the world's particle physics community, work on experiments conducted at CERN.
The acronym originally stood, in French, for Conseil Européen pour la Recherche Nucléaire (European Council for Nuclear Research), which was a provisional council for setting up the laboratory, established by 11 European governments in 1952. The acronym was retained for the new laboratory after the provisional council was dissolved, and informally changed to Centre Européen pour la Recherche Nucléaire (European Centre for Nuclear Research).
The accelerator complex
The CERN accelerator complex has six main accelerators:
- Two linear accelerators generating low energy particles for injection into the Proton Synchroton. One is for protons and the other for heavy ions. These are known as Linac2 and Linac3 respectively.
- The PS Booster , which increases the energy of particles generated by the linear accelerators before they are transferred to the other accelerators.
- The 28 GeV Proton Synchroton (PS) built 1959.
- The Super Proton Synchrotron (SPS), a 2 km diameter circular accelerator built in a tunnel, which started operation in 1971. It originally had an energy of 300 GeV (but has been upgraded several times). As well as having its own beamlines for fixed-target experiments, it has been operated as a proton-antiproton collider, and for accelerating high energy electrons and positrons which were injected into the Large Electron Positron (LEP) collider.
- Isotope Separator On-line (ISOLDE), which was used to study unstable nuclei and first commissioned in 1967. Particles are initially accelerated in the PS Booster before entering ISOLDE.
The accelerator of the future: the LHC
Construction of the CMS detector for LHC at CERN
Most of the activities at CERN are currently directed towards building a new collider, the Large Hadron Collider (LHC) and the experiments for it, due to start operation in 2007. This will use the 27 km circumference circular tunnel previously occupied by LEP which was closed down in November 2000, and the PS/SPS complex to pre-accelerate protons which will be injected into it. The tunnel is located 100 m underground, in the region between the Geneva airport and the nearby Jura mountains. Four experiments (CMS, ATLAS, LHCb and ALICE) are currently being built, and will be running on the collider; each of them will study particle collisions under a different point of view, and with different technologies. Construction for these experiments needed an extraordinary engineering effort. Just as an example, to lower the pieces for the CMS experiment into the underground cavern which will host it, a special crane will have to be rented from Belgium, which will be able to lift the almost 2000 tonnes of each piece. The first of the approximately 5,000 magnets necessary for construction was lowered down a special shaft at 1300 GMT on March 7, 2005.
- The original linear accelerator (Linac1).
- The 600 MeV Synchro-Cyclotron (SC) which started operation in 1957 and was shut down in 1991.
- The Intersecting Storage Rings (ISR), an early collider built in 1966
LEP, an electron-positron collider which started operating in 1989.
- Low Energy Antiproton Ring (LEAR), commissioned in 1982. This assembled the first pieces of true antimatter, in 1995, consisting of nine atoms of antihydrogen. It was closed in 1996, and superseded by the Antiproton Decelerator .
As the SPS and the LEP tunnels cross the Franco-Swiss border, there are several experimental areas on the French side in addition to the main site which is in Switzerland for legal purposes (although since 1965 it actually occupies land on both sides of the border).
There is also the Antiproton Decelerator (AD), which reduces the speed of antiprotons (which are created travelling at nearly the speed of light) for research into antimatter.
The smaller accelerators are located on the main Meyrin site (also known as the West Area), which was originally built in Switzerland alongside the French border but has since been extended to span the border. The French side is under Swiss jurisdiction and so there is no obvious border within the site, apart from a line of marker stones. The only access to the site from France is via a customs manned post which can only be used to for transferring equipment between the Meyrin site and other CERN sites in France. This is in fact the only permitted route for such transfers. Under the CERN treaty, no taxes are payable when such transfers are made. Personnel travelling between the sites without equipment must use the normal customs posts on the border and enter or leave the Meyrin site via the entrance in Switzerland.
The SPS and LEP/LHC tunnels are located underground almost entirely outside the main site, and are mostly buried under French farmland and invisible from the surface. However they have surface sites at various points around them, either as the location of buildings associated with experiments or other facilities needed to operate the colliders such as cryogenic plant and access shafts. The experiments themselves are located at the same underground level as the tunnels at these sites.
All of these experimental sites are in France, although some of the ancillary cryogenic and access sites are in Switzerland. The largest of the experimental sites is the Previssin site, also known as the North Area, which is the target station for non-collider experiments on the SPS accelerator. Other sites are the ones which were used for the UA1, UA2 and the LEP experiments (the latter which will be used for LHC experiments).
Outside of the LEP and LHC experiments, most are officially named and numbered after the site where they were located. For example, NA32 was an experiment looking at the production of charmed particles and located at the Previssin (North Area) site whilst WA22 used the BEBC bubble chamber at the Meyrin (West Area) site to examine neutrino interactions. The UA1 and UA2 experiments were considered to be in the Underground Area, i.e. situated underground at sites on the SPS accelerator.
Computer Science and CERN
The World Wide Web began as a CERN project, initiated by Tim Berners-Lee in 1980. Based on the concept of hypertext, the project was aimed at facilitating sharing information among researchers. The first website went on-line in 1991. On April 30, 1993 CERN announced that the World Wide Web would be free to anyone.
The original CERN signatories were:
Federal Republic of Germany,
- The United Kingdom,
Bringing the current number of member countries to 20.
-  According to Lew Kowarski, a former director of CERN, when the name was changed, the acronym could have become the awkward OERN, Heisenberg said "But the acronym can still be CERN even if the name is ... ."