Scientists preparing to build linear collider of the next generation

This illustration depicts an unusual subatomic particle collision with 400 giga-electron volts of energy, which the Collider Detector at Fermilab detected. The proposed linear accelerator would be capable of generating particle collisions at even higher energies, reaching 500 giga-electron volts or more. The two straight lines show tracks left by a Z particle that has transmuted into an electron and an anti-electron.

Major discoveries in high-energy physics a decade from now likely will depend on the construction of a multibillion dollar linear accelerator capable of producing an intense beam of electrons and positrons with a diameter that will measure one thousandth the width of a human hair.

Building such an accelerator would pose a significant technological challenge, said Melvyn Shochet, the Elaine and Samuel Kersten Jr. Distinguished Service Professor in Physics and the College. But at stake could be the discovery of new subatomic particles, extra dimensions in the universe or even critical clues about the long-sought Unified Field Theory, which would describe how the universe works in a single equation.

“The most pressing issue in the field is trying to understand the physics that we believe is right over the horizon,” Shochet said. And physicists believe dramatic discoveries will come within their reach at the energy scales that new accelerators have begun to achieve. That is why the High Energy Physics Advisory Panel’s Subpanel on Long-Range Planning, a group charged with developing a 20-year plan for the future of high-energy physics, has recommended that the United States join an international effort to build a linear accelerator over approximately the next decade.

University physicists have played key roles in the discussions leading up the recommendation, which was submitted in January to the U.S. Department of Energy and the National Science Foundation. Shochet and Rocky Kolb, Professor in Astronomy & Astrophysics and the College, were among the 24-members of the High Energy Physics Advisory Panel’s Subpanel on Long-Range Planning.

Also contributing to the process was Mark Oreglia, Professor in Physics and the College and co-chair of the U.S. Linear Collider Stewardship Committee, who organized a Linear Collider Workshop in January at the Gleacher Center that attracted more than 200 physicists from around the world. At the workshop, physicists discussed the potential technology and designs that might be used for the new accelerator.

The most advanced technology thus far has been developed by physicists at DESY, the German high-energy physics laboratory. “They’ve demonstrated that a workable machine can be built for roughly five to seven billion dollars,” Oreglia said.

The linear accelerator, if built, would compliment the Large Hadron Collider, now under construction at CERN, the European Laboratory for Particle Physics. Physicists are likely to make major discoveries with the LHC later this decade, if not sooner at Fermi National Accelerator Laboratory’s newly operational Tevatron, Shochet said.

But understanding those discoveries in detail will require data that the LHC will be unable to provide, he explained. An electron-positron linear accelerator would not only be able to produce more types of particles that physicists are interested in studying, but it also would produce them more cleanly than the LHC.

The HEPAP subpanel has recommended that the United States make a bid to build the new linear accelerator in this country. Two potential sites would be near Fermilab or the Stanford Linear Accelerator Center in California. Physicists in Japan and Germany, meanwhile, propose building the accelerator near Tokyo or Hamburg, respectively.

“Everybody’s thinking of the Superconducting Super Collider and how not to make the same mistakes that were made there,” Oreglia said. Construction on the SSC, at a location south of Dallas, was halted in 1993 after an expenditure of $2 billion.

Shochet explained that the approach being taken to build the proposed linear accelerator is different than the SSC, which failed in part because it was a “pseudo-international project. First we decided what accelerator we were going to build, and then we looked for international partners, asking, ëwhy don’t you help us pay for it?’ It’s understood that this time it’s got to be truly international from the start.”

The HEPAP subpanel has estimated that if the collider were built abroad with U.S. support, the U.S. high-energy physics budget would need a 10 percent increase over the next 20 years, Shochet said. Building the collider in the United States would require a 30 percent budget increase.

“This is in an environment where over the last decade, the support of physical sciences has dropped by 20 percent,” Shochet said.

What is needed is a funding increase for all of the physical sciences as well as for particle physics, he said.

“There has been a very successful increase that was clearly needed for biological sciences research over the past decade. That has been quite important to the health of the nation, to the health of the biological and medical sciences,” Shochet said.

Harold Varmus, a Nobel laureate in medicine and former director of the National Institutes of Health, has written in The New York Times about the importance of addressing funding disparities in the sciences. Varmus wrote that medical advances such as Magnetic Resonance Imaging often flow from the work of physicists, chemists or engineers.

“The point he was making is that each field of science is really interdependent on all other fields of science,” Shochet said. “What we’re really pushing for is a broad funding increase in the physical sciences.”