On the Trail of the Bashful W

Reporting the discovery of a much sought elementary particle

As the shirtsleeved, tousled-haired physicist bounded across the platform, he unleashed his ideas in staccato bursts and gesticulated with the verve of a maestro. "You have to pardon Carlo," said a colleague. "He's a little high-strung these days." With good reason. Using one of the world's most powerful atom smashers, Italy's Carlo Rubbia, 48, and his team of 134 European and American scientists appear to have snared a trophy that has been the dream of physicists for two generations: discovery of the so-called W particle, the elusive carrier of one of the universe's basic forces.

Rubbia's announcement last week at a meeting of physicists in New York City brought instant speculation about Nobel Prizes for him and key colleagues. The detection of the W particle is an example of extraordinary scientific sleuthing, comparable to finding a missing person in a crowd of a billion people. It also provides dramatic new support for a keystone of contemporary physics: the idea that nature's fundamental operations can be united in a single mathematical framework.

Einstein spent the second half of his life futilely trying to unify two of nature's basic forces: gravity, the glue that holds the universe together, and electromagnetism, which governs such familiar processes as fire, chemical reactions, even human metabolism. But there are two other less well-known agencies at work within the nucleus of the atom: the so-called strong force, which binds the nucleus' protons and neutrons, and the weak force, which shows its hand in the disintegration, or "decay," of certain nuclei, like those of uranium 235. Post-Einstein theorists in the late 1960s succeeded in finding a unity between electromagnetism and the weak force. Their "electroweak" theory postulated the existence of a family of three particles called intermediate vector bosons (after the Indian physicist S.N. Bose).

The bosons, known as W- and W+ and ZDEG, are carriers of the weak force, just as photons transmit the electromagnetic force. But bosons are more elusive than photons. Although nearly 100 times as heavy as protons, they could not be forged in any existing accelerator. While physicists in the U.S. and elsewhere began designing new machines, Rubbia, who divides his time between Harvard and CERN, the French acronym for the Geneva-based European Organization for Nuclear Research, decided that there must be an easier, cheaper way. He persuaded CERN to let him modify its major accelerator, the Super Proton Synchrotron, to achieve higher energies. Instead of sending nuclear bullets, protons, barreling into a fixed target, the four-mile circular atomic race track was redesigned so that two sets of bullets--protons and their antimatter opposites, antiprotons--raced around it in opposite directions. At two junctures their paths intersected, producing collisions of great violence.

Rebuilding the accelerator took five years and $100 million. The particles had to be confined to their separate tracks until the critical moment when enough antiprotons were created to make collisions likely. Sensitive detectors had to be devised that could spot a single boson. (In a typical run, the scientists figured that they would get just one boson in a billion collisions. It would also be extremely shortlived, vanishing in less than a billionth of a billionth of a second.) When the CERN machine went back on line last fall, reaching energies of more than 540 billion electron volts, Rubbia's team identified at least five collisions that indicated the presence of both W+s and W-s. They did not, however, find any ZDEGs.

Even rival American physicists were impressed. At Fermilab, the big U.S. accelerator center outside Chicago, Chris Quigg whimsically conceded, "They walk like Ws and talk like Ws." Rubbia was both ebullient and philosophical. Noting that scientists have been chopping matter into ever finer pieces since the time of the Greeks, he said, "We may not yet be at the end of the ladder." This file is automatically generated by a robot program, so viewer discretion is required.