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Linear thinking. Planned collider would smash electrons into positrons.

Particle Physicists Chart the Future

SNOWMASS VILLAGE, COLORADO--High-energy physicists from around the world would like to build a multibillion-dollar linear collider as the next big accelerator project. The unexpected consensus, cobbled together at the end of a 3-week summit that concluded on 21 July, failed to address a competition between three countries to host the machine--and whether any of the governments would be willing to pay the lion's share.

Such a linear collider would take electrons and their antimatter twins, positrons, and smash them together. Because electrons and positrons are fundamental particles--indivisible "leptons"--their collisions are much less complicated than collisions between other particles. This simplicity, along with scientists' ability to manipulate the electrons' polarization, gives electron-positron colliders the ability to make much more precise measurements than composite, or hadron, colliders. The sacrifice is that they operate at lower energies--a handicap in searching for massive particles. But in the past few years, particle physicists have become convinced that the Higgs boson, a long-sought particle responsible for objects' mass, should be within reach of a new electron-positron collider.

Enticed by this prospect, the community made an unofficial decision to back the collider rather than scrabble for funding of other potential facilities. An estimated price tag of at least $6 billion makes it extremely unlikely that one country will be willing to pay for the facility. But the opportunity to host it is believed to be a major attraction.

Physicists from Europe, Japan, and the United States each want their own country to win the honor. Talk in the hallways pegged Hamburg, Germany, and Batavia, Illinois, as the leading contenders for the site of the accelerator, to the chagrin of Japanese scientists. But these differences are unlikely to be serious stumbling blocks. "It's more important to get a machine built than to get it built in the U.S.," says Ken Bloom, a physicist at the University of Michigan, Ann Arbor.

A bigger issue for U.S. scientists is whether their government will be a reliable partner. The U.S. withdrawal from the International Thermonuclear Experimental Reactor still hurts (Science, 9 October 1998, p. 209), and a White House budget official who addressed the conference gave little indication that money would be forthcoming. Given the current budget situation, said Mike Holland of the Office of Management and Budget, some politicians are likely to ask: "What would be the impact on society if the funding for high-energy physics were zeroed out?"

Related sites

The Snowmass Summer Workshop Web site
News article about new colliders from the Fermi National Accelerator Laboratory
TESLA, the international plan for a new linear collider