Cern (European Laboratory for Particle Physics)

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CERN (EUROPEAN LABORATORY FOR PARTICLE PHYSICS)

CERN is the everyday name of the European Laboratory for Particle Physics located near Geneva in Switzerland, but the acronym actually stands for Conseil Européen de la Recherche Nucléaire (European Council for Nuclear Research). This Council was set up in 1952 to establish the European Organization for Nuclear Research that came into being in 1954 when the agreement establishing CERN was signed by the participating member states. The Council stressed the "necessity to build a laboratory for the high energy study of elementary particles in western Europe," and its advice was followed.

Whereas the first model for such a laboratory was the Brookhaven National Laboratory in the United States, only its academic (high-energy physics) part was deemed appropriate for an international venture. CERN provides scientists from its member states with experimental facilities for the study of high-energy physics. At the end of the twentieth century, CERN included twenty member states: Austria, Belgium, Bulgaria, the Czech Republic, Denmark, Finland, France, Germany, Greece, Hungary, Italy, the Netherlands, Norway, Poland, Portugal, the Slovak Republic, Spain, Sweden, Switzerland, and the United Kingdom. All countries agree on a yearly budget, which was approximately $600 million in 2001 and which is shared by the member states in proportion to their respective net national income.

Belgium, Denmark, France, Germany, Greece, Italy, Norway, the Netherlands, Sweden, Switzerland, the United Kingdom, and Yugoslavia created CERN in 1954. Austria quickly joined, but Yugoslavia withdrew for financial reasons. The core group of twelve member states throughout the sixties and seventies was eventually joined by Spain and Portugal in the eighties and by the Central European countries in the early nineties, soon after the fall of the Berlin Wall. Finland joined at the same time and was followed by Bulgaria, the latest member. CERN was also the first international organization in which postwar Germany participated. Besides providing access to unique facilities and making it possible to participate in great scientific achievements, member states participate in a highly successful European organization conducive to creating better links between European nations.

As it grew in size, CERN became international in another aspect. Although the official location of the organization is in Switzerland, the Laboratory now extends well into neighboring France, and two of its machines straddle the Franco-Swiss border, with accelerated particles crossing it several thousand times per second.

The Goal of CERN, Its Machines, and Its Users

World War II had left continental Europe in a state of scientific inferiority. The creation of CERN responded to the desire of European physicists to establish in Europe, as had been established in the United States, a frontier domain of research. However, there were technical, financial, and political roadblocks to overcome in creating such a large international scientific laboratory. The latter were removed after the encouraging address of Isidor I. Rabi at the UNESCO conference of 1950. Pierre Auger and Eduardo Amaldi took care of the former. These three scientists are considered the founding fathers of the organization.

CERN developed rather quickly into a large laboratory with first-class resources, some of them unique in the world, but it took many years to reach research parity with the United States. This was achieved in the early eighties, and since then there have been more American physicists using CERN than European particle physicists using American facilities (in particular, Brookhaven, the Stanford linear accelerator, and Fermilab).

The goal of CERN was to study the deep structure of matter, an academic domain requiring large facilities in which cooperation and collaboration could easily prevail over competition. The term "nuclear," which appears in the name of the organization, comes from the fact that nucleons were still considered the basic building blocks of matter in the 1950s. However, research was quickly oriented primarily toward high-energy particle physics, and the first big CERN accelerator to be built was the proton synchrotron (PS), which followed a smaller machine, the synchro-cyclotron (SC). The PS was commissioned in 1960 shortly before the Brookhaven Alternating Gradient Synchrotron (AGS). Both accelerators used a new strong focusing technique and thus reached energies over 25 giga electron volts (GeV).

CERN's Intersecting Storage Rings (ISR) were completed in the early seventies. This machine, unique in the world, provided head-on collisions between protons accelerated in the two rings to energies up to 31 GeV. The resulting collision energy was equivalent to that of a 2,000 GeV machine using a fixed target but with a very low intensity. The CERN Super Proton Synchrotron (SPS) came into operation in 1977, five years after its American counterpart at Fermilab. Its transformation into a proton-antiproton collider in the early 1980s resulted in the attainment of the highest energies accessible at that time, with colliding beams of 300 GeV. The next big CERN machine was the Large Electron Positron Collider (LEP), an electron-positron collider with 100 GeV, and later 200 GeV, of collision energy. It operated from 1989 to 2000. The Large Hadron Collider (LHC) is under construction and will begin operation in 2007. It will collide protons at 14 tera electron volts (TeV) and will be the highest-energy machine in the world. The SPS and LEP are, respectively, 7 and 27 kilometers in circumference and are both located in underground tunnels.

CERN does not carry out research on behalf of its member states. It builds and operates facilities that are open to external users from universities and research laboratories. Physicists represent a minority (about 10%) of CERN's 2,500 employees, and most of the CERN physicists hold nonpermanent positions. The number of scientific users has steadily climbed from 1,500 at the commission of the SPS in the midseventies to over 6,500 in 2002. There were very few scientific users from nonmember states in the sixties, but their number quickly increased to about a third of the present total. In particular, the uniqueness of certain facilities (the ISR, the proton-antiproton version of the SPS, LEP, and now the preparation of the LHC experiments) has attracted many American groups. From an initially primarily European center, CERN has now grown into a laboratory serving a worldwide community. In 2002 half of the high-energy physicists in the world were CERN users.

Nuclear physicists have been attracted by the heavy ion and muon beams as well as by the Low Energy Antiproton Ring (LEAR), a facility providing beams of low-energy antiprotons, and by ISOLDE with its on-line study of radioactive isotopes. The advent of colliders (with beams accelerated in opposite directions and clashing in special zones), as opposed to accelerators using fixed targets, has imposed the use of very big detectors dwarfing even the giant bubble chambers of the sixties and seventies. Detectors are built by large collaborations (hundreds of physicists for LEP and over a thousand for the LHC), and the dominant fraction of their cost (around 80 percent) is borne by different funding agencies. The detectors are assembled at CERN from components built all over the world.

Research at CERN

Research at CERN has long paralleled research in the United States. Thanks to CERN, European scientists did well in the 1960s and 1970s, hunting new particles, studying hadron and neutrino interactions, elucidating the nature of weak and strong interactions, and collecting evidence for the quark structure of matter; however, CERN was following rather than leading. European physicists contributed much to these experiments, but the Nobel Prize discoveries (the two neutrinos, the track chamber hunt of hadron resonances, the discovery of CP violation and that of the surprising new J/ψ particle, the quark structure of the proton as first seen in electron scattering, and the discovery of the tau lepton) came from America.

The first significant CERN discovery in this competitive race was the electron decay mode of the pion, which had resisted discovery efforts in the United States. Results at the ISR did not reach the Nobel Prize level, but the 1973 discovery of the weak interaction with neutral currents could have. The research group working on the big heavy liquid bubble chamber, Gargamelle, was led by André Lagarrigue, who sadly passed away soon afterward. However, the major discovery of W and Z, the vector bosons of the weak interaction, was made possible with the use of the CERN proton-antiproton collider. This research brought the 1984 Nobel Prize in Physics to Carlo Rubbia, the project leader, and to Simon van der Meer, who had designed a clever way to build an intense antiproton beam, which was later used at the Fermilab Tevatron. These two discoveries, made a decade apart, vindicated the theory of the electroweak interaction and provided clear evidence for hadronic jets in hadronic collisions, which had been predicted by quantum chromodynamics (QCD). With these results, CERN could claim some world supremacy in the field of high-energy physics.

LEP was built to test with precision the Standard Model of fundamental particles and fundamental interactions, which combines the electroweak interaction and chromodynamics, thus bringing unity and simplicity at the quark-lepton level to the structure of matter. LEP succeeded very well but without bringing the hoped-for surprises that could have heralded a departure from the predictions of the Standard Model. Research at LEP stopped with only a hint that the Higgs boson (the missing element in the Standard Model) could be there at the very limit of the energy available on the machine. The top quark was discovered at Fermilab, but its mass could be predicted from the very precise LEP data. Even though the LEP energy was not sufficient to produce a topantitop pair (which was possible using the Fermilab Tevatron), the presence and mass of the top quark could be inferred from the precision measurement of other processes.

LEP was shut down for the construction of the LHC, which will explore fertile new ground. The heavy-ion program, pursued since the mid-1980s, could provide evidence for the formation of a new state of matter at very high temperatures where quarks are no longer confined within hadrons but can briefly roam freely over the volume of colliding ions. This research, now being pursued at the Relativistic Heavy-ion Collider (RHIC) at Brookhaven, will continue at the LHC, at increased energies, when the LHC is completed. This transition between free to bound quarks played a key role in the evolution of the universe 10 microseconds after the Big Bang.

Opening Up to the World

CERN was built to bring European scientists together, working on a common endeavor, soon after they had been on opposing sides during World War II. This it did remarkably well, and several other European scientific organizations, modeled after CERN, were created dealing with astronomy, space research, and molecular biology. There is no experiment at CERN that does not involve scientists from several nations.

CERN opened, maintained, and encouraged cooperation with the East, in particular with the international laboratory at Dubna, near Moscow, and with the Soviet laboratory at Serpukhov. Exchanges of scientists quickly developed, and this had a noticeable and highly positive impact as mutual understanding and appreciation prevailed over lack of knowledge and mistrust. It was very important to maintain this scientific collaboration during the Cold War, and this contributed to the eventual thaw in the political climate. It was quite natural for the Central European countries to join CERN in the early 1990s, basing their new membership on already existing collaborations. CERN has many users from the new independent states of the former Soviet Union.

The laboratory opened beyond Europe with many scientists coming from the United States, Japan, China, and India. They all work together, learn physics from each other, and also learn each other's cultural ways. Financial contributions for the construction of the machines, besides those naturally associated with the detectors, come from the United States, Japan, and other countries. In the case of the United States, this tallies surprisingly well with the European contribution to the Hubble telescope.

The success of CERN taking a leading role in particle physics worldwide is largely due to the fact that the laboratory grew up in one place. Although this resulted from the impossibility of reaching an agreement on a new site for the SPS in the 1970s and from the advent of affordable tunnel boring techniques that allowed big machines to be built in suburban areas, this fixed location paid strong dividends as the construction of new machines exploited previous ones, and an imposing, stable infrastructure was built up, along with a highly competent staff. A unique network of interconnected machines, each one feeding the next, made it possible to build LEP and then the LHC without an increase of the annual budget. The PS and the SPS will serve as the injector for the LHC, which will use the LEP tunnel and the LEP cryogenics infrastructure. The cost of the LHC is therefore half of what it would have been in a new location.

A New Style of Work

Particle physics at CERN has gradually shifted to the use of very large detectors built and operated by imposing collaborations. This is a new style in physics research. It has its drawbacks when compared to the smaller congenial and flexible teams of the past. Nevertheless, there are three positive elements. First, despite the size of the collaboration, it is always possible to see who has done what so that individual recognition is possible within the large collective effort. Research could not work otherwise. Second, working on such large and highly sophisticated facilities, with tight schedules and in an international atmosphere, has a very high training value much appreciated in industry. Indeed, half of the new Ph.D.s working on LEP for their degree have turned to industry where their acquired skills are appreciated. This is a very important spin-off of this academic research. The age distribution of CERN users, which has been stable over the LEP decade, shows a peak at 28, a 10-year expanse in width, followed by a plateau at about half the peak height and extending until retirement age. This shows explicitly that training through research has become as important as training for research even at this advanced level. This is welcome since this research with large facilities requires far more young people than academia can eventually absorb. Finally, this concentration of skills in large collaborations, with a critical assessment of new ideas and an urge to achieve what is needed for the research, is highly conducive to new technical developments. It is not a surprise that the World Wide Web was born at CERN.