Science: Getting to the heart of matter

Will the particle physicists at CERN find the essence of everything?
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GREATER fleas have lesser fleas and so ad infinitum, thought the satirist Jonathan Swift. The physicist's equivalent of the rhyme is that atoms have protons and neutrons, and that they in turn have quarks, and that quarks ... well, we don't know. It is the task of a massive apparatus now being constructed at CERN, the European Laboratory for Particle Physics in Geneva, to find out.

From 2005, the $6bn (pounds 3.75bn) Large Hadron Collider (LHC) will start running experiments. "Hadrons" are physicists' classification of the group of heavy subatomic particles including protons and neutrons, and which are composed of quarks. However, it's only feasible to accelerate protons, because they're electrically charged.

The LHC is designed to produce collisions between protons at unprecedentedly high energies. The wreckage from such collisions is expected to reveal whether quarks are elementary particles, and in the process to generate exotic new particles. The first of its giant superconducting magnets, each the size and weight of a loaded truck, was delivered at Christmas and is now being tested.

The LHC nearly never happened, however. CERN was plunged into gloom for much of last year because of budget cuts by contributing countries. But then two things happened. CERN obtained its first major funding from outside Europe. It is one of the main achievements of Christopher Llewellyn Smith, the Briton who is departing as CERN's director-general, to bring the Americans and Japanese, long present in the teams of scientists performing experiments, on board as financial contributors.

Second, after several false starts, CERN's member state delegates managed to agree in December on his replacement. Professor Luciano Maiani, president of Italy's National Institute of Nuclear Physics in Rome, will take over from Llewellyn Smith in 1999.

The recently signed deals will now allow the LHC to be completed three years earlier than originally planned. "For the first time, the US government has agreed to contribute significantly to the construction of an accelerator outside our borders," said the US Energy Secretary Federico Pena, agreeing a package of more than $500m.

The move would not have come without the US government's decision in 1993 to axe its own planned Superconducting Supercollider (SSC). That project might have gone ahead - and probably put CERN out of business - had it been proposed as an addition to an existing institution, such as the Fermilab outside Chicago. In the event, it fell victim to the hubris of Texas politicians who wanted a brand new facility in their own back yard.

CERN was set up in order to recover Europe's "natural" dominance in particle physics after the US took the lead during the Second World War. It has historically defined itself in competition with American laboratories, as is described in The Quark Machines, published last year by the Institute of Physics. The book is an account by Gordon Fraser, the long-time editor of the CERN Courier, the centre's respected in-house journal. And it has scored well in this competition, making breakthroughs despite (or because of) national differences.

Some of CERN's success arises because each new experiment builds on the last. The LHC will use the 27km-diameter underground particle track and other components of the current Large Electron-Positron collider (LEP), for example. "Without the tunnel I think it would have been impossible to have the LHC," says Maiani. The American effort, spread between Fermilab, Berkeley in California, Brookhaven on Long Island and other institutions, cannot economise in this way.

In the short term, Maiani must ensure "a lively scientific atmosphere" during CERN's years as a building site before the LHC is completed. One planned experiment involves building a long-range neutrino experiment. The neutrino-generating end of the apparatus will be at CERN, the detector will be 400 miles away 1,400 metres under Gran Sasso in the Apennines near Rome, a formation of rock with naturally low background radioactivity which already houses a solar neutrino detector. The experiment aims to discover whether neutrinos, which have no electric charge, even possess mass.

Another research theme is the so-called quark-gluon plasma. The gluon is the massless carrier of the strong force that bunches the quarks in atomic nuclei in groups of three for each proton and neutron. "When you see an atomic nucleus made up of protons and neutrons, you see a collection of little bags within each of which these constituents are confined," Maiani explains. "If you increase the pressure or the temperature, you diminish the distance between each bag, and in the end the bags fuse. Then the constituents can move from one bag to another and you have created a new state of matter. The energies reached in the LHC should be sufficient to create this fusion at the centre of the collisions."

This fusion will model what happened during the first microseconds in the formation of the universe as the quark-gluon plasma cooled and coagulated to form familiar protons and other particles. The element of competition will be present in both experiments, with similar research programmes in the US and Japan providing a spur to the CERN effort as well as mutual confirmation of results.

Although it will not run until after his term of office, Maiani's first priority remains the LHC. Its experiments represent a huge increase in complexity even for the 10,000-strong community at CERN: while LEP teams numbered several hundred, up to 2,000 scientists will collaborate on the LHC experiments.

"The LHC is a considerable improvement over the LEP machine in two senses," Maiani explains. "First, with an increase of energy you can produce more heavy particles, and in the energy range which can be explored with LHC we expect to find the supposed Higgs Boson responsible for the interaction on which the generation of particle masses depends. The Higgs Boson is the one missing element in the Standard Model [the consensus view of subatomic particles and forces], and that we have to find.

"Then there is another factor. Since quantum mechanics determines that the wavelength associated with a particle decreases with increasing energy, we have to go to higher energies in order to see in finer detail the structure of the elementary particles. Maybe, we will arrive at the point at which the particles which appear elementary today will reveal an internal structure. That happened in the past with the atom and with the proton. Both were considered elementary but then revealed hidden structure. We don't know whether this will happen with the quark."

So the particles we today call fundamental may not be fundamental at all? "That's certainly a possibility." And is there no theoretical lower limit on the size of particles? Absolutely not, says Professor Maiani. Quarks really could have lesser quarks and so ad infinitum. This is bothersome for those who would like to reach a state of final certainty about the building blocks of matter, but it is good news for institutions like CERN, helping to ensure their long-term future.