DOWN THE LINE: The 3.2-kilometer-long tunnels of the Stanford Linear Accelerator Collider would be dwarfed by the proposed International Linear Collider, which would be five times as long. Image: LINDA A. CICERO Stanford News Service
High-energy physicists have a new machine in mind: an unprecedented accelerator 30 kilometers long that would offer a precise tool to explore some of the most important unanswered questions in physics. But the specter of the defunct Superconducting Supercollider--and the money the project ended up wasting--looms large. Advocates of the machine, however, think they can overcome national doubts by going global.
Since they first began discussing a linear collider in earnest at a 2001 conference at Snowmass, Colo., the world's physicists have consistently and vigorously planned an international effort. Their hopes recently rose when U.S. Secretary of Energy Spencer Abraham named it the highest "midterm" priority in a 20-year outlook of new science facilities. The report estimates that were the project to be approved and funded, peak spending would occur sometime between 2010 and 2015.
The vision is of one machine built by the world and shared by the world. "Many people have been working very hard to make this more than an empty slogan," says theorist Chris Quigg of the Fermi National Accelerator Laboratory in Batavia, Ill., because no one government seems likely to spend the estimated $5 billion to $7 billion that such a facility would cost.
The plan is to accelerate electrons and positrons (the antimatter version of the electron) down dual 15-kilometer pipes and smash them together inside a large detector. The total energy would be up to one trillion electron volts (TeV). This energy may appear much less than the 2-TeV Tevatron at Fermilab and the 14-TeV Large Hadron Collider to be completed at CERN in 2007, but because the particles in those machines share their energy among their constituent quarks, their effective energy drops by about a factor of 10. By design, the international linear collider will have higher interaction rates, and because the spins of the particles in its beams are aligned¿ something that cannot be done at the Tevatron or Large Hadron Collider¿it will be much more precise in dissecting and analyzing particle interactions.
The collider could reveal the specifics of Higgs bosons (particles that imbue all other particles with mass) and light supersymmetric particles (shadowy particles such as the neutralino, which may account for the dark matter that constitutes 23 percent of the universe). That knowledge could in turn open the door to exotica such as extra dimensions and low-energy superstring phenomena. "That¿s the exciting thing about the linear collider," says theorist Joseph Lykken of Fermilab. "It gives you a window into this whole other realm of physics that we¿re really interested in."
But opening that window requires cold, hard cash. The last time particle physicists asked for dollars for an accelerator, two billion of them ended up underneath the Texas prairie in now water-filled tunnels meant for the Superconducting Supercollider. "The story of its demise is so complicated, it¿s fair to say it died of fluctuations," Quigg remarks. "Our community hopes to have learned from the experience to organize future projects so they will be less vulnerable to fluctuations and political tussles."
In fact, several groups in the U.S., Europe and Japan are committed to the linear collider. "We are all behind it," states Albrecht Wagner, director of the DESY high-energy laboratory in Hamburg, Germany, acknowledging that in the end the project¿s site will be a political decision, not unlike that now being made about the fusion reactor called ITER.
So far the early politics involve technology
recommendations. To accelerate particles,
DESY backs a superconducting, lower-radio-frequency
cavity; a higher-frequency, room-temperature
structure is being championed by
a collaboration between the Stanford Linear
Accelerator and the KEK Accelerator Laboratory
in Tsukuba, Japan. Given the history
of grand accelerators, deciding on which approach
to take will no doubt be the easy part.
David Appell is based in Lee, N.H.