Next month, figures from the worlds of physics, politics and beyond will gather in Geneva to celebrate the 50th anniversary of CERN. As they toast half a century of European collaboration and achievement in particle physics, including two Nobel prizes and the invention of the Web (see “CERN at 50: the highlights”), those assembled will inevitably start thinking about the future of the lab. Will the Large Hadron Collider (LHC) be finished on time? Will it find the Higgs boson? And what will CERN be like 50 years from now?

The origins of CERN are generally traced back to 1949, when the French theorist and Nobel laureate Louis de Broglie proposed setting up a new European laboratory to halt the exodus of physics talent from Europe to North America. A year later, at a UNESCO conference in Florence, the American Nobel-prize winner Isidor Rabi put forward a resolution calling on UNESCO “to assist and encourage the formation and organization of regional centres and laboratories in order to increase and make more fruitful the international collaboration of scientists”.

The resolution was unanimously adopted and, after two more UNESCO conferences, 11 European governments agreed to set up a provisional Conseil Européene pour la Recherche Nucléaire (CERN). The new council met in Amsterdam and a site near Geneva in Switzerland was selected. By 1953 the physicists who would build CERN’s first accelerators had already started collaborating with their opposite numbers at the Brookhaven lab in the US, although the new laboratory did not formally come into existence until the CERN convention was ratified by the first 12 member states on 29 September 1954. The new lab was called the Organisation Européene pour la Recherche Nucléaire but it has been known as CERN ever since.

Initially the European lab found it difficult to compete against Brookhaven and was beaten to the punch by its US rival on several occasions. But bolstered by the discovery of weak neutral currents in 1973 and the W and Z bosons in 1983, confidence grew and the Geneva laboratory is now a magnet for particle physicists from around the world (see Further information and “CERN, the US and the W”). Indeed, there are now more Americans working at CERN than there are Europeans at particle-physics labs in the US. And when the LHC starts colliding beams of protons at an energy of 14 TeV (14 x 10¹² eV) in 2007, CERN will have the high-energy frontier to itself for at least a decade.

Aymar makes his mark

In June the CERN council agreed a new seven-point strategy for the laboratory. Completing the LHC on schedule in 2007 is the top priority, followed by consolidating the lab’s infrastructure to guarantee reliable operation of the LHC; examining the lab’s experimental programme apart from the LHC; co-ordinating research in Europe; building a new injector for the LHC in 2006; increasing R&D on the Compact Linear Collider (CLIC); and working on a long-term strategy for the lab.

The man charged with making sure that all of this happens is Robert Aymar, who started a five-year term as director general of CERN in January. Although Aymar is not a particle physicist, he is no stranger to the LHC. He chaired the committee that assessed and recommended the project for approval in 1996 and also led the external review committee that was set up in 2001 when it became clear that the LHC was behind schedule and over budget.

That committee’s recommendations – to delay the start date from 2005 to 2007 and to cut back on all non-LHC activity – were accepted by the CERN council in March 2002. The lab also borrowed €300m from the European Investment Bank to pay for the SwF 2.9bn (about €1.9bn) accelerator. When detector costs, computing costs and the money spent by the member states and others are all added up, the total price tag is about SwF 5bn. One thing that CERN does not have to build is a new tunnel: the LHC is being installed in the same 27 km circular tunnel that housed the highly successful Large Electron Positron (LEP) collider.

So is the LHC on track and on budget? “Yes,” says Aymar. “It is now on schedule to be completed in 2007 within the new cost to completion.” And what are the biggest challenges between now and 2007? “The detectors are on schedule but there is no ‘float’ or slack in the schedule. However, it is possible to start with a detector that is not 100% complete and finish it after the first experimental run. The situation is different for the accelerator – the final bolt has to be in place for the accelerator to work. For now, the manufacturing of every component is on time.”

One problem has been that some of the companies supplying components for the LHC have gone out of business. “This happens most months,” Aymar says matter-of-factly. However, the biggest difficulty so far has been the delay in fitting the distribution line for the liquid helium that will cool the accelerator’s 6000 superconducting magnets to just 1.9 K. This has, in turn, held up the installation of the magnets, because the distribution line cannot be accessed once the magnets have been positioned in the tunnel.

Brian Foster of Oxford University, chairman of the European Conference for Future Accelerators (ECFA), recognizes these problems: “There are always irritating things that go wrong in large projects like the LHC, sometimes with hi-tech components and also with low-tech stuff like welding.” However, Foster is also confident that the LHC will come online in 2007.

The delays in installing the magnets have forced CERN to store many of them above ground, which was never intended. This is not a trivial matter because there are 1232 dipole magnets, each 15 m long. Moreover, the magnets, which will bend the two beams of protons in opposite directions around the ring, will now have to be installed in two or three different sectors of the tunnel at the same time, rather than sector by sector as originally planned.

To overcome these problems, more staff – both accelerator-magnet specialists from CERN and contractors from industry – will be needed to install the magnets. CERN now faces a choice: it either has to borrow staff from other accelerator labs or cancel the fixed-target experiments at its other accelerators in 2006 (see below). A decision is expected before the end of the year. Aymar says he is concerned about the problem but that he is confident it can be solved without having to delay the start of LHC operations.

Watching the detectors

Meanwhile, the LHC’s four detectors – ATLAS, CMS, ALICE and LHCb – are on schedule to “close” by April 2007, according to Jos Engelen, chief scientific officer and deputy director general at the lab. “Now that they are in the production phase it is possible to follow their progress quite accurately,” he says, “but there is no slack in the schedule and there is no scope for mishaps.”

ATLAS and CMS are massive “general-purpose” detectors for particle physics that will be used to search for the Higgs boson and supersymmetric particles (see “The LHC detector challenge”). With masses of 7000 and 12 500 tonnes, respectively, ATLAS and CMS are two of the biggest and most sophisticated pieces of physics kit ever built.

Elsewhere, the LHCb experiment will measure aspects of charge-parity (CP) violation – the process that is thought to explain why the universe is made of matter rather than antimatter – that cannot be measured by the “B-factories” at the Stanford lab in the US and KEK in Japan. The ALICE experiment will also study proton-proton collisions, but its main goal will be to collide lead atoms together to produce a quark-gluon plasma – a novel state of matter in which quarks are no longer confined inside larger particles. A smaller experiment called TOTEM will be installed near the CMS detector to measure the total collision rate, which is an important measurement in any new energy range.

The biggest obstacle on the detector front is being faced by the CMS collaboration, which needs 75,000 lead-tungstate crystals to make high-resolution measurements of photon energies. There are already 40,000 crystals at CERN, but the Russian factory that is supplying them can only produce 1200 per month, which will not be enough to complete the detector on time. CERN initially agreed a price with its Russian supplier – a military firm that was going commercial with help from the European Union – but the company is now trying to increase the price. CERN hopes to bring in two other suppliers to introduce commercial competition and increase capacity.

Getting to know the Higgs

So what about the physics: will the LHC find the Higgs boson, the particle that is thought to be responsible for other particles having mass? Engelen thinks that it will. “The success of the Standard Model in explaining the results of so many experiments needs the Higgs boson, and the Higgs mass is like the last piece in the jigsaw,” he says. “LEP showed that the Higgs was heavier than 114.4 GeV, and we can also guess its mass from other experiments. Within the Standard Model we know that it is not heavier than 240 GeV at the 95% confidence level. That makes me very confident that we will find the Higgs boson, or, if there is no Higgs mechanism, that we will be able to understand how symmetry is broken in nature to generate the mass of particles.”

The Higgs signature depends on its mass. A relatively light Higgs with a mass of about 120 GeV will decay into pairs of B-mesons, tau leptons or photons, which will be easy to produce but hard to detect among the background of other processes and particles. If the Higgs is heavy, about 160 GeV, it will decay to pairs of W or Z bosons. These will be harder to produce, says Engelen, but easier to spot. If there is no Higgs mechanism, the LHC will see scattering events between pairs of W bosons that would otherwise be “absorbed” by the standard Higgs mechanism.

But there will be more to finding the Higgs than measuring its mass. “We want to measure its coupling to other particles,” says Engelen, “and to understand how it decays to other particles.” The ultimate goal, however, is to measure the Higgs potential, which will involve producing two Higgs bosons to see how they interact with each other. (The Higgs potential, which is shaped like a Mexican hat, explains why the Higgs field has a non-zero value in the vacuum.)

Engelen says that the LHC will only be able to produce pairs of Higgs bosons if the Higgs mass is less than 500 GeV. However, measuring the Higgs potential will also require precision measurements for which “the LHC does not provide the ideal environment”. A linear electron-positron collider of high enough energy would be better suited to such measurements.

However, he is less confident about finding evidence for supersymmetry – the theory that predicts that all fundamental particles have “superpartners” with different spins (see “CERN: the next 50 years”). “Supersymmetry is a theoretical idea that is attractive for several reasons – dark matter, unification of the forces, explaining the mass hierarchy – but is not compelling in the way that the Higgs is,” Engelen says. “New physics needs to happen between 100 GeV and 10¹⁵ GeV to get the forces to unify, and there are crude theoretical arguments that suggest that there is a threshold at about 1 TeV.”

A neutral supersymmetric particle would interact very weakly with ordinary matter, so it could only be detected by looking for any “missing” transverse momentum in collisions. This approach is already used to detect neutrinos, which have similarly weak interactions with matter. The initial transverse momentum at the LHC will be zero, so the sum of the transverse momenta of all the particles produced in any collision should be zero as well. If it is not, then a supersymmetric particle might be responsible. However, there is no classic signature for supersymmetric particles like there is for the Higgs. “That is where the creativity of the experimenters comes in,” says Engelen.

Besides the Higgs and supersymmetry, ATLAS and CMS will also measure various properties of the top quark and explore the strong interaction at 14 TeV. “This is not as important as the Higgs,” says Engelen, “but it is still important. Analysis of the data from the LHC will keep us off street corners for a long time to come.” Handling all the data from the LHC will also require a completely new approach to computing dubbed the “Grid”.

Back to basics

The protons involved in collisions at the LHC will have already passed through four accelerators before they reach the giant collider. They start in a machine known as Linac 2 and are then accelerated to progressively higher energies by the Booster, the Proton Synchrotron (PS) and Super Proton Synchrotron (SPS) before arriving at their destination.

Some of these machines date from 1959, and, not surprisingly, basic components such as coils, power supplies and electronics are prone to failure. In the past the lab has tended to repair equipment after it has failed, rather than maintaining it. Aymar now wants to increase maintenance to ensure that he LHC works reliably.

And once the accelerator is up and running, CERN will start to think about the work needed to increase the luminosity. A new linear-accelerator injector will be built during 2007-2010 to replace Linac 2, and the lab will explore the possibility of replacing the Booster with a Superconducting Proton Linac (SPL). In addition to its role in the LHC, the SPL could be used for neutrino physics and nuclear. A decision on the SPL is expected in 2010.

Many of the buildings at the laboratory also need extensive maintenance – “It sometimes rains inside, and windows have fallen off,” says Aymar – but this is unlikely to be tackled until after the LHC is paid for in 2011.

Another challenge for the Geneva lab is to increase its small non-LHC research programme, which was cut back to help pay for the new accelerator. Currently this work includes a “fixed-target” programme at the SPS, nuclear physics, work on anti-atoms, and the construction of a facility that will send a beam of muon neutrinos to the Gran Sasso laboratory, some 730 km away in Italy, in 2006. However, the only non-LHC work planned for next year are nuclear-physics experiments with rare isotopes at the ISOLDE facility.

“We are looking for ideas for an exciting new non-LHC programme rather than a business-as-usual approach,” says Engelen. Astroparticle physics would seem an obvious area to move into, and some astroparticle-physics experiments are already “recognized” by CERN, but Engelen says that the lab has no big ambitions in this area.

One for all – or all for one?

One of the more controversial elements of CERN’s new seven-point strategy is its intention to have a role in the “co-ordination of research in Europe”. CERN has traditionally been responsible for designing and building accelerators, and has played only a limited role in the detectors, which are run and built by a large number of labs across Europe. Aymar would now like to see more collaboration in the design and construction of accelerators as well, with other labs sharing more responsibility. This would, he adds, help to rebuild accelerator skills and knowledge outside the large accelerator labs like CERN.

As examples of co-ordination, Aymar cites the Co-ordinated Accelerator Research in Europe (CARE) project, which could contribute to an upgrade of the LHC in about 2012, and EUROTeV, which is investigating generic R&D issues related to a possible future linear collider. “CERN’s new co-ordination role will not mean giving orders”, says Aymar, “but it will allow long-term plans and priorities to be established for the discipline across the whole of Europe.” He adds that CERN’s ambitions will not clash with the role of the European Conference for Future Accelerators (ECFA) because the CERN council includes representatives of the funding agencies that actually pay for the machines, as well as particle physicists.

But is there a conflict between the council running CERN as a lab in it own right and its co-ordination role, which could involve overseeing competition between CERN and other particle-physics labs like DESY in Germany? After all, there are sure to be fewer big accelerators in the future than there are now. “I do not see it like that,” says Aymar. “People should not think that there is a ‘CERN view’. CERN is just a place where big machines can be built – its ownership is distributed across Europe. CERN should not be in competition with other European accelerator labs. The real competition”, he says, “is between ideas within a co-operative framework.”

ECFA chairman Brian Foster agrees that CERN needs to rethink its role and relationships with the rest of the particle physics community. “CERN needs to be imaginative and creative in this area,” he says. “CERN is an excellent laboratory and the LHC will be the dominant facility in particle physics for 15-20 years, but it will not be possible for every large accelerator to be built at CERN.”

Linear thoughts

Where CERN does seem to be in competition with the rest of the particle-physics community is the question of what should be the next big accelerator after the LHC. The ECFA and its equivalents in the US and Japan have stated that a “sub-TeV” linear collider – a 500 GeV electron-positron collider that could be upgraded to 1000 GeV (1 TeV) – should follow the LHC.

However, CERN wants any decision about constructing a linear collider to wait until 2010, even though an International Technology Recommendation Panel (ITRP) is due to decide between different approaches to a sub-TeV collider before the end of this year. CERN is keen for its own Compact Linear Collider (CLIC) technology, which is potentially capable of reaching 3-5 TeV, to have time to demonstrate that its novel two-beam approach to particle acceleration is feasible before any irreversible decision to construct a lower-energy collider is taken.

“There is a large community that is enthusiastic about a linear collider,” says Engelen, “but no major funding agency or nation has stood up yet and taken the lead in committing a major fraction of the resources required for such a project. CERN would prefer for a decision to wait until 2010 because we would know more about the Higgs and the best energy for a linear collider – a 600 GeV Higgs would be embarrassing for sub-TeV linear collider. In 2010 we will also know if CLIC will work – I am sure that it will.”

An “accelerated R&D effort towards CLIC” is the fifth point in the new CERN strategy. Historically, the CLIC project has had an annual budget of SwF 3m per year, with about 25 staff working on it, but it is going to receive an extra SFr 30m plus 100 man-years’ effort between now and 2009. Most of the extra resources are coming from outside the CERN budget.

ITRP chairman Barry Barish of Caltech still believes that a 500-1000 GeV linear collider should be the next big machine for particle physics, but he stresses that it is important to keep other options open. “All evidence points to the new physics we seek in the 500-1000 GeV energy range,” he says, “but we will know once the LHC is doing physics. This is really a probe into the unknown, and our best guidance could be wrong – that is why we need to keep our options open until the LHC is operational.”

Even if all goes to plan for CLIC, it could not come online before 2021 at the earliest. As for where CLIC might be built, Aymar says that CERN will certainly bid to host it.

An efficient future

In his first message to CERN staff as director general, Aymar acknowledged that CERN is perceived as a place of privilege. “CERN has been lucky in the support it has received from member states,” he says. “They have provided continuity in funding for physics and in making decisions – there are lots of labs where this has not happened. We should show that we recognise this by producing results, and by being efficient and organized.”

Might this involve a reduction in staff? “Staff numbers have been reduced continuously and considerably over the last decade and the current staff head count is the minimum needed for the current programme, and is probably too small,” he says. “There are areas like technology transfer were a small number of extra staff could make a big difference.”

And what about the lab’s famously high salaries? A CERN fellow in their early 30s with a PhD can expect to take home about SwF 6000 per month. “In physics we are in competition with other labs for the most brilliant people,” says Aymar, “so we need to pay a premium to make sure we get the right staff, although we could discuss the size of the premium. It is the same with engineers, where we are in competition with industry. To get the best people you have to know what the competition is paying and set your salaries accordingly.”

The final item in CERN’s seven-point strategy is to prepare a comprehensive review of the lab’s long-term activity. Aymar says that this review, which will be available by 2010, will cover funding, global capacity and the plans of the member states, as well as physics. “We need to avoid what is happening in neutrino physics,” he says, “where there is too much redundancy between experiments of similar potential.”

How do others see the future of CERN and particle physics in Europe? Will there still be two big particle labs in Europe in 2050? “I think there will,” says Foster. “DESY will have a small particle-physics activity, but it will be much broader, doing all sorts of accelerator-based stuff including free-electron lasers. CERN will still be a major, and probably the dominant, particle-physics laboratory in the world – it will be a bit more diverse than now, but probably not much.”

By the time he retires at the end of 2008, Aymar hopes to have achieved three things. “I want to make sure the LHC is running reliably and that its performance is improving to the design values and better. I also want to improve the culture of the lab, making it more goal-oriented and more cost-conscious. Lastly I want to prepare it for the future.”

Further information

CERN at 50: bringing nations together

It is often said that CERN helped to bring Europe together after the Second World War, and East and West together after the Cold War. “I fully subscribe to this theory, even if I have no ‘scientific’ proof of it,” says Jos Engelen, CERN’s chief scientific officer, who first came to the lab in 1971. “There is something magic about the atmosphere at CERN – you learn how to collaborate. Today you can see Indians and Pakistanis working together, and students from the United Arab Emirates working with physicists from Israel.”

Former CERN director general Herwig Schopper agrees. “It is not well known that CERN was established with two objectives: to promote science and to bring nations together,” he says. “I am convinced that all the money that has been spent on CERN is justified by what has been achieved in improving understanding between nations.”

The 12 member states that signed the CERN convention in 1954 were Belgium, Denmark, France, Germany, Greece, Italy, the Netherlands, Norway, Sweden, Switzerland, the UK and Yugoslavia. Since then Yugoslavia has left and Austria, Spain, Portugal, Finland, Poland, Hungary, Slovakia, the Czech Republic and Bulgaria have all joined, bringing the number of member states to 20. Spain actually left CERN in 1969 but rejoined in 1983. India, Israel, Japan, the Russian Federation, Turkey and the US all have observer status, as do the European Union and UNESCO.

It is estimated that about half of the 13,000 particle physicists in the world are involved in experiments at the lab. Some 4499 come from the 20 member states, and there are also large contingents from Russia (744), the US (586) and Japan (103).

CERN also brings European countries together in more obvious ways. Part of the laboratory is in Switzerland and part is in France. The main site at Meyrin straddles the border, but you can only enter and leave through the main gate, which is in Switzerland, although the French president Charles de Gaulle is said to have entered and left the main site through a gate on the French side of the border. There is also a second site at Prevessin in France.

Most of the 27 km long Large Hadron Collider will be in France: the control room will be at Prevessin and all the detectors, apart from ATLAS, will also be on (or under) French soil. One little-known fact is that there is a special tunnel that goes from the Meyrin site, under the St Genis road, and emerges in France. The tunnel is under CERN’s control, but is restricted to authorized personnel and all material transported through it is recorded.