The next era of high-energy physics will come into sharp focus this weekend when an international team of physicists unveils a proposal for a major linear collider.

Linear thoughts: DESY staff assemble prototype accelerator parts for the proposed TESLA collider. Credit: DESY

The team, based at the DESY particle physics laboratory near Hamburg, will propose the construction of a machine called TESLA — the Tera electron volt Energy Superconducting Linear Accelerator — at an estimated cost of about US$3 billion. The machine would be a linear electron–positron collider based on superconducting resonators (also known as 'cavities'). It would allow particles to collide at energies of between 500 and 800 giga-electron volts (GeV).

The announcement will attract keen global interest because both the United States and Japan believe they should host the next major collider project. Physicists from both countries have been jointly developing a proposal for a linear collider that would meet similar energy goals to those of TESLA using conventional, rather than superconducting, resonators to accelerate the electrons. The project is known in the United States as the Next Linear Collider (NLC) and in Japan as the Japan Linear Collider (JLC).

The various teams, all of them international, are downplaying the competitive aspect, but each community of physicists would obviously like the next-generation machine to be built on its own territory. Both the United States and Japan are making substantial contributions to another major project, the Large Hadron Collider (LHC) that is being built at CERN, the European Laboratory for Particle Physics, near Geneva. Construction of TESLA in Germany, with the LHC also in Europe, could mark the virtual eclipse of particle physics in the United States and Japan for a generation.

A linear collider would help physicists to discover what lies beyond the standard model, the theory that describes all elementary particles and the corresponding forces between them. Many aspects of the theory have been fully validated. But one exception is the Higgs boson, the heavy particle that physicists hope to find using either the renovated Tevatron at Fermilab in Illinois (see Nature 409, 754–755; 2001) or the LHC.

Both these accelerator rings, which create collisions of heavy particles such as protons, may detect evidence for supersymmetry, a theory that would augment the standard model by finding corresponding 'sparticles' for each known particle. But proton colliders produce messier and more complex collisions than electron–positron colliders, which have long been used to complement them in particle physics investigations.

“The LHC will provide one view beyond the standard model and the electron– positron collider will provide another,” says Burt Richter, former director of the Stanford Linear Accelerator Center (SLAC) in California, which has led the US arm of the NLC design.

Both TESLA and the NLC would achieve high enough energies — in the 500 GeV to 1 TeV (× 1012 eV) range — to complement the LHC. But the NLC design uses conventional technologies developed at SLAC and at the Japanese laboratory KEK, which are based on copper resonators. NLC advocates say that this will allow the machine to operate at higher frequencies, yielding faster acceleration and a smaller, and therefore potentially cheaper, facility than TESLA.

Another advantage of the NLC design is the technology's established track record. “We already have one at 50 GeV, so going to 500 GeV is only a factor of 10, and we have lots of experience,” says Richter.

But the NLC concept received a blow in the past year, when researchers found physical deterioration in the copper cells after 1,000 hours of operation. “We should know by the summer if new designs will overcome these problems,” says Steve Holmes, associate director at Fermilab.

More ominously, an initial 1999 cost estimate for the NLC came in at a politically unrealistic $7.9 billion. “We need this to be reduced by 25%, preferably by 50%,” says Peter Rosen, head of high-energy physics at the US Department of Energy. He says a potential reduction of 30% has already been achieved.

TESLA's use of superconducting resonators should mean a higher beam intensity and lower operating costs, its advocates say. Compared with the NLC, the radiofrequency devices that excite superconducting resonators are simpler to build. But the largest functioning accelerator using superconducting technology, the Thomas Jefferson National Accelerator Facility in Virginia, operates at only 1 GeV.

Albrecht Wagner, DESY's director, believes that the price estimate his team will publish on 23 March will be considered reasonable. But unlike the US estimate, it will exclude labour and operational costs, which could double the actual price.

The TESLA proposal will be assessed by the Wissenschaftsrat, Germany's science council, which will decide whether to recommend it to the government. German research minister Edelgard Buhlman has made positive noises about TESLA, but has said the project will go ahead only with the support of the international particle physics community — and financial support from abroad. But Wagner contends that construction could start within two years.

Political factors are likely to settle the choice of both the site and the design. The US community plans a major gathering of particle physicists in Snowmass, Colorado, this July to look at future priorities. A sub-panel of the High Energy Physics Advisory Panel is meanwhile mapping out a 20-year plan for the discipline.

With substantial funding allocated for building the LHC, Europe is not flush with money for a new collider either, and DESY is trying to promote TESLA as a multidisciplinary facility whose associated free-electron laser will also be used by materials scientists, chemists and biologists.