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At several locations around a track, the particles are either smashed into metallic targets or steered to collide head-on with one another. Most of the new machines opt for the collision technique, which produces more energy. Explains Alvin Tollestrup, a Fermilab physicist: "It's the difference between a semi crashing into a small car and two semis crashing head-on." Some of the tremendous energy of those impacts is fleetingly transformed into strange particles that are thought to have existed in the very first moments of the universe. Before the unstable fragments decay back into energy and more familiar bits of matter, their feathery traces are recorded by detectors.
Those traces have helped physicists to track down more and more members of the large and seemingly limitless bestiary of subatomic particles. Last year, for example, Rubbia shared a Nobel Prize for having discovered, using the CERN super proton-antiproton synchrotron accelerator (SPPS), the W and Z particles. His finding provided proof for a theory that united two of the fundamental forces, electromagnetism and the weak force.
The payoff from the SSC should be even greater. As it is now conceived, the accelerator would generate energies of 40 trillion electron volts, in contrast to the 640 billion electron volts produced by CERN's SPPS accelerator. More impressive still, it would produce collisions 20 times as powerful as the generation of big machines now under construction at CERN, Fermilab and the Stanford Linear Accelerator Center. Whizzing past each other, the SSC's two opposing beams, consisting of closely packed bunches of about 10 billion protons each, would complete about 3,000 laps a second. In four to six places around the ring, the beams would intersect, producing up to 100 million collisions a second. At each collision site, a highly sophisticated detector at least three stories high would be needed to sense and record the impacts, telltale debris and any newly created particles.
The SSC is by no means a certainty. Critics are worried that its cost will drain money from other worthwhile projects, and growing concern about the federal deficit could, at best, delay congressional approval. But many scientists are convinced that the big collider will eventually be built. Says James Cronin, a physicist at the University of Chicago: "If we're serious about finding out about nature, we have to do it."