19.8 News Feat CERN MH

news feature

The show CERN goes on

CERN, the centre for particle physics in Europe, has been smashing its way through the subatomic world for the past 50 years. Alison Abbott finds out what’s in store for the future.

uring CERN’s routine maintenance shut-down in 1999, acrobats and Dmime artists turned one of the vast halls within the laboratory’s 27-kilometre tunnel into a stage. Light and shadows played around the nine-storey cavern, illuminating a poetic ballet of aerial gymnastics. On ropes, trapezes and ledges, the performers enacted Paul Dirac’s creative struggle with his 1920s theory of antimatter and his pessimistic belief that such theories could never be con- firmed experimentally. In the show’s final scene, the huge backdrop parted to reveal the DELPHI experiment, where for the past decade CERN physicists have been observing Where art and science meet: the DELPHI experiment takes a starring role in a dance about antimatter. collisions between electrons and positrons, their antimatter counterparts. deep and fundamental questions with which the lab over the past half-century, and The show symbolized everything that the laboratory concerns itself — What is our exchanged views in its famous cafeteria, and CERN has achieved in its first 50 years (see Universe made of? How did it arise? — but they’ll wistfully recall a touch of magic. “The ‘50 years of CERN’, below). The lab’s raison also in the idealism of its scientific approach, intense but non-aggressive scientific style,the d’être has been to develop increasingly and the charm of its working atmosphere. extraordinary variety of international scien- sophisticated machines to provide answers Founded in the ruins of post-war Europe tists — I loved it, and it completely changed to the questions that plague theorists seeking as a cross-border partnership to recreate the my perspective,”says Harry Nelson, a particle fundamental truths about the Universe. base in particle physics destroyed by the Sec- astrophysicist at the University of California, If science ever comes close to poetry, it ond World War,CERN continues to live by its Santa Barbara,who spent three years at CERN does here, in the ugly sprawl of CERN’s flat- philosophy that science has no borders. in the late 1980s as a postdoc.“And it’s a place roofed buildings overlooked by the beautiful Ask any of the tens of thousands of physi- where some really great discoveries have been

Jura mountains near Geneva. Not just in the cists from 80 countries who have worked at made.I sometimes dream of going back.” LEFT) CERN/SPL;(FROM CERN

But will the accolades still be coming in

CERN when CERN celebrates its 75th anniversary?

The technical demands of particle physics ARKER/SPL

have increased at an alarming rate — D. P much to the dismay of governments that have to pay for machines that now cost bil- lions. As purse-strings tighten, stresses have emerged in the traditionally cohesive international particle-physics community. The community is expected to announce its technology choice for the next big machine by the end of this week. Despite the CERN’s director-general, Robert Aymar, is responsible for ensuring the success of the lab’s next big display of unity, behind the scenes CERN is machine, the Large Hadron Collider, which will hunt the Higgs boson (simulated, right). gambling that an alternative technology it is developing will, at some future date, become and then capture the resulting fireworks with great discoveries, the heavy W and Z particles, a scientifically superior option. cleverly designed detectors. The properties of carriers of the weak nuclear force, just five newly discovered particles fed back into theor- months apart in 1983. This established CERN Early days ies that became collectively known as the stan- as a world leader,and won Rubbia and van der For its opening act, in the early 1950s, the dard model of the structure of matter. Meer the 1984 Nobel prize in physics (see mood was upbeat. The concept of CERN was CERN’s first machine, the Synchro- ‘Winning personalities’,overleaf). first proposed by the French physicist and Cyclotron, accelerated a beam of protons up Nobel prizewinner Louis de Broglie at the to energies of 600 million electron volts (eV) Upping the ante 1949 European Cultural Conference in Lau- and smashed it into a fixed target. This rela- CERN’s most recent machine, the Large sanne. Five years later, 12 states signed the tively low collision energy was sufficient to Electron Positron (LEP) collider, whose 27- founding treaty, making CERN the first post- generate pions, unstable particles formed kilometre tunnel straddles the Franco-Swiss war organization to include West Germany from a mixture of matter and antimatter. border, hurled a beam of electrons into a as a member. CERN now has 20 member The CERN pioneers were thrilled to watch beam of positrons. Unlike protons, elec- states, and although the Soviet Union never pions decay into electrons and neutrinos in trons have no internal structure, so their joined, many of its scientists worked there line with predictions from the standard collisions are less messy, although their alongside Westerners during the cold war. model. Each new machine took collision lighter mass means that they cannot reach Back in 1954, the frontier of knowledge energies higher, revealing new particles with such high collision energies. Still, LEP was was nuclear, not particle, physics, as CERN’s properties predicted by the standard model. able to better characterize particles that had full name,the Conseil Européen CERN’s second act opened been discovered with the SPS, and was only pour la Recherche Nucléaire, “The non-aggressive in the early 1980s with techno- switched off in 2000 to make room in the reflects. Theorists recognized scientific style, the logical innovation. In the late tunnel for its successor, the Large Hadron three fundamental forces gov- variety of international 1960s, CERN accelerator physi- Collider (LHC). Until the LHC starts oper- erning atomic matter — the scientists. I loved cist Simon van der Meer had ating in July 2007, only a handful of small strong nuclear interaction, the CERN, and it developed a key technology, experiments are running at the lab. weak nuclear interaction and completely changed called stochastic cooling, for As the machines get bigger, so do the col- the electromagnetic force — my perspective.” storing antimatter particles.This laborations.Rubbia’s W and Z team involved but had little idea of how to inte- — Harry Nelson made it possible to collide a beam 150 scientists. Today, teams at accelerator grate them in a way that would of protons precisely with a beam labs often number 500. The biggest experi- explain the physical Universe. of anti-protons travelling in the opposite ment planned for the LHC, called ATLAS, But they had some idea about what was direction. If both beams are accelerated to involves 2,000 physicists. missing. Although only protons, neutrons similar speeds,the collision energy is doubled. Although the numbers may sound fright- and electrons had been described as the basic In the 1970s, the experimental physicist ening, those working in big collaborations constituents of an atom,cosmic-ray research Carlo Rubbia, who held joint positions at say that individuals are not condemned to had shown that there were a lot more exotic CERN and Harvard University, championed anonymity. Michel Spiro, now director of particles, with names such as ‘pions’ and this high-stakes technology. And in 1981, the National Institute of Nuclear and Particle ‘muons’,to be discovered. CERN upgraded its Super Proton Synchro- Physics in Paris, remembers working on The best way to make discoveries was to tron (SPS) into a collider able to reach ener- the W and Z experiment: “Rubbia was smash a beam of charged particles,such as pro- gies of up to 500 billion eV. number one, of course, but I made my own

(FROM LEFT) D.(FROM PARKER/SPL; CERN tons or electrons, into a target at high speed With its souped-up SPS,CERN scored two contribution which was recognized by my

NATURE | VOL 430 | 19 AUGUST 2004 | www.nature.com/nature 825 © 2004 Nature Publishing Group news feature colleagues.” And it all happened “in an theories such as ‘super- atmosphere of thrilling enthusiasm”, he strings’ and ‘extra dimen- CERN adds,“because we knew that the experiment sions’to try to explain how could be a breakthrough for particle physics”. the Universe may fit In the ATLAS collaboration,experiments together, but they are very are split into subprojects. Karlheinz Meier speculative,” says John of the University of Heidelberg, a principal March-Russell, a theoreti- investigator in ATLAS,says his own ‘Trigger’ cal physicist at the Univer- project, which will design an electronics sys- sity of Oxford, UK, who tem to filter out the most interesting physics spent four years at CERN. from LHC collisions, involves only 30 physi- Like his colleagues, he cists from five institutes.“It’s sort of like the hopes that the LHC will old days,”he says.“The group is small and we help reduce speculation. are getting to know each other very well.” “Knowing more about Brain food: cafe society is at the heart of CERN’s relaxed atmosphere. Project teams are scattered geographi- the Higgs and supersym- cally, but share information over the World metry will let us pose the Wide Web, invented at CERN for this pur- next questions more sensi- pose.In future they will use the Grid,a global bly,” says Frank Wilczek, a supercomputing network that CERN is theoretical physicist at the Q. SCHIERMEIER developing to handle and distribute the vast Massachusetts Institute of data sets that the LHC will spew out. Technology. As CERN reaches this Universal truths dramatic crunch point — The next half-century will be dedicated to if the LHC does not find the research into the big unknowns. To complete Higgs, particle physics will the standard model, physicists predict the be thrown into crisis — it existence of one more particle, called the takes centre stage in parti- Higgs boson, which is needed to explain why cle physics. No other orga- particles have mass. Other theories that hope nization has won political to extend the standard model predict ‘super- support for such a massive, Surf’s up: the World Wide Web was devised at CERN. symmetrical’ partners of the known particles yet esoteric,project. at higher masses. These particles have not yet The first sign that particle physicists had whom come from CERN member states. been seen, but they should be created by the priced themselves out of the market came in This international mix will continue high-energy collisions, accelerating protons 1993, when the US Congress pulled the plug CERN’s ideal of science without borders up to 7 trillion eV,within the LHC. on the planned Superconducting Super- for at least another two decades. “We have Discovering particles is one collider,also designed to chase the Indians working on the same LHC experi- way to answer deeper questions “Knowing more Higgs. US physicists were glad ments with Pakistanis, Chinese with Tai- about the Universe. We now about the Higgs and that CERN member states held wanese, Israelis with Arabs,” says CERN’s know that the standard model supersymmetry will faith, because it gave them the current director-general, Robert Aymar. describes barely 5% of the Uni- let us pose the next opportunity to keep working. “This ‘romance’ of CERN, the way it con- verse. The rest is invisible to us. questions more And when the LHC’s finances tributes to good relations, is not fading — Some of this is thought to be sensibly.” looked wobbly in 2001, the quite the opposite.” composed of ‘dark matter’,which —Frank Wilczek United States, Japan and Russia Aymar’s reputation is built on his man- is apparent only through its grav- pitched in with in-kind contribu- agement skills for large projects; most itational pull and which might include tions amounting to 12% of the overall build- recently he headed the international ITER supersymmetrical particles. This was joined ing costs of SFr3.2 billion (US$2.5 billion). project to build a prototype fusion reactor. in 1998 by the even more mysterious ‘dark CERN still pays the lion’s share towards the He is a pragmatist,who was brought in by the energy’, whose existence was needed to LHC’s infrastructure, but the detectors that CERN council to restore political confidence explain observations that the rate at which will record the collisions are being built by 500 in the LHC. Since his arrival in January he the Universe is expanding is accelerating. research institutes around the world from has restructured top management at the lab Theoretical physicists are already work- their own budgets. These institutes also pro- to ensure an iron grip on LHC development ing on ideas that go beyond the standard vide most of the 5,000 or so physicists who will and costs. The collider’s finances are now

model. “We have worked on overarching conduct the experiments, only two-thirds of assured,thanks to a system of bank loans that LEFT) CERN;(FROM HEINEKEN

must be paid back by the end of the decade. The world’s most expensive ground-based Winning personalities science kit “will stay on target and within CERN garnered two Nobel prizes in physics in The W and Z discoveries, and many others, budget”,Aymar promises. its first 50 years, won by three very dissimilar would not have been possible without an earlier “CERN will only be free to get involved in characters. Simon van der Meer, from the CERN invention for which Georges Charpak won other projects after 2011, when the LHC Netherlands, and Carlo Rubbia, an Italian, the 1992 prize. Charpak’s ‘multiwire proportional debts are paid off,”he adds. This is a crucial shared the 1984 prize for the discovery of chamber’ replaced photographic methods for point, because CERN must think about life the W and Z bosons. Van der Meer was as particle detection with electronic ones, improving beyond the LHC, which is expected to shy as he was brilliant and inventive, whereas both sensitivity and spatial resolution. operate until 2020, and possibly to 2025. Rubbia’s acknowledged genius was allied to Charpak, born in Poland and now a French The global physics community has already a powerful personality. citizen, spent some of his earlier life in the French decided what machine it wants next, an Van der Meer shunned all publicity, whereas resistance and in the Dachau concentration electron–positron collider that will be able Rubbia became director-general of CERN from camp. Elegant and charming, Charpak was to characterize more precisely the particles 1989 to 1994. His excitable nature generated reputedly ham-fisted in the lab and gave a that the LHC discovers. The machine of some tension, but was offset by his impulsive handsome portion of his winnings to the choice is a linear collider that can reach genius, say some former colleagues. technician who had helped him out. A.A. higher energies with electrons than did the circular LEP. A higher energy range also means greater if built, should be sited in Geneva, CLIC’s Two designs for such a sub-TeV linear chances of spotting more supersymmetrical new lease of life has ruffled the feathers collider, which will achieve energies just particles. And if the LHC sees no hint of the of many of those involved in developing below 1 trillion eV,are on the table.The ‘cold’ Higgs or supersymmetry, then the case for a collider technology. design, which depends on superconducting sub-TeV machine looks distinctly weak. Part of the discontent is down to a percep- technology, is led by DESY in Hamburg, and But all things are not equal. The CLIC tion outside Europe that CERN wants to the ‘warm’ option by US and Japanese labs. technology is far less advanced than the other consolidate its present leading position,even The International Technology Recommen- designs.Until Aymar arrived,the project was if this is at the cost of the well-being of the dation Panel of the International Linear Col- progressing in a leisurely fashion towards a US particle-physics community, which, lider Steering Committee met in Korea on feasibility decision in 2013. He has brought most agree, will suffer if all the big machines 11–13 August to select one of these options this forward to 2009. continue to be located elsewhere. for development by a global collaboration, On balance, CERN’s chances of hosting with hoped-for operation in 2015.As Nature Future plans the next big accelerator are slim, so when it went to press,it was expected to announce its This date is crucial. By then the LHC could celebrates its 75th anniversary in 2029, it is decision this week at the International Con- have glimpsed the Higgs boson, and CERN likely to be a very different place. The stream ference on High Energy Physics in Beijing. will be almost free of its debts. The design of visiting scientists will have reduced to a This timetable would seem to rule out phase of the sub-TeV machine will also be trickle and the exciting discoveries will be CERN as a host for the proposed machine, advanced, but it is unlikely that any country taking place elsewhere. Nevertheless, Aymar but with Aymar’s arrival the stakes have been will have committed itself to the project’s is positioning CERN for a leading role in raised. Since 1986, CERN has been develop- biggest expense — its construction. If feasi- any future machine, wherever it might be ing an alternative linear collider design called bility studies show CLIC to be viable, it located. He says he wants any European the Compact Linear Collider (CLIC). In a could present itself as an alternative. Spiro, participation to be funnelled through standard collider, the electromagnetic waves who now heads the French delegation to CERN, rather than through national agen- that accelerate the beams are created within CERN, is a strong believer in this strategy. cies or governments. special cavities called klystrons. Instead, “It would be better than committing to a Even if CERN were no longer in the fore- CLIC uses a second set of intense low-energy less ambitious machine,”he says. front,could its unique spirit relocate to the lab beams to provide the waves that the accelera- But it’s a long shot. Even if CLIC were hosting the next big accelerator? Probably, ting electrons surf.This allows it,in theory at shown to be feasible,it could not start opera- although some worry that if current problems least, to achieve much greater accelerations. ting until 2021 at the earliest, a long time for with visas continue, this would hamper any It may even be possible to achieve energies of even particle physicists to wait. And the idea international project located in the United between 3 trillion and 4 trillion eV. of building a sub-TeV machine first and States. In the meantime, the place where the Most physicists agree that, all things CLIC later is not politically viable. World Wide Web was born, and where fresh being equal, CLIC makes more sense scien- Although Aymar stresses that CERN’s insights into the Universe will be argued over tifically. If the Higgs boson turns out to be decision to accelerate CLIC should not influ- in that most celebrated of cafeterias,is set for a heavier than expected, a sub-TeV machine ence plans for the sub-TeV collider, and he glorious finale. ■

CERN may not be powerful enough to analyse it. has never suggested that a CLIC machine, Alison Abbott is Nature’s senior European correspondent.