Nature's Onion

In applied (or misapplied) physics, the ugly implications of the Soviet resumption of nuclear testing still made the splashiest news of the week. It took physicists themselves to appreciate the larger implications of a much quieter announcement: the discovery of the omega, a new subatomic particle that exists for an infinitesimal fraction of time on the strange borderline between matter and energy. The track of the evanescent omega may some day lead scientists toward a new level of physical understanding.

No one will ever see the little particle, but theoretical physicists--those mystic prophets of science--calculated several years ago that an unknown heavy meson probably can exist. Like the neutron, they figured, it would have no electric charge, so it would leave no track in a cloud or bubble chamber. They were sure it would disintegrate so quickly that other signs of its brief career would be hard to find. But the theoreticians considered the undiscovered particle so important that they named it omega in advance, implying that it might be the last unknown particle left in nature's locker.

Curved Prongs. The predicted difficulty of spotting omega proved to be only too real. At least five search parties in separate laboratories reported no luck. Then, under the leadership of Yugoslav Physicist Dr. Bodgan C. Maglic, scientists at the University of California's famed Lawrence Radiation Laboratory analyzed 2,500 photographs of the four-prong stars found when antiprotons shot from Berkeley's bevatron accelerator collide with protons in a bubble chamber. Each star shows four curved lines made by negative and positive pions (pi mesons) created by the collision. There seemed to be a slight chance that careful examination would show that in some cases some of the star lines were formed by the disintegration of an extremely short-lived intermediate particle.

Hopefully, the photographs were fed into "Franckenstein," a machine developed by Lab Mechanic Jack Franck, which automatically measured the curvature, angle and length of the star's lines and recorded the data on a punched card. Then Professor Arthur H. Rosenfeld fed the cards into a digital computer set up to search for stars that suggested the presence of an invisible intermediate particle. Only 93 of the 2,500 stars showed the computer what it was looking for. Carefully reexamined, the stars proved that when an antiproton hits a proton, it sometimes creates five mesons--two positive pions, two negative pions and one pion with no charge at all. For a fleeting instant, one positive and one negative pion cling to the uncharged pion, forming a single unit. That unit lives for only 10^2^2 (one ten-thousand-billion-billionth) seconds. It travels only one ten-billionth of a centimeter before it disintegrates. But in the precise world of physics, this short life is enough to get a particle classed as actual matter. The Berkeley physicists decided that their invisible particle was the long-sought omega.

Job Eternal. Despite its name, omega will probably not be the last new particle to be discovered. Physicists now believe that protons may contain as many subatomic particles as the 90-odd chemical elements that were once thought to be the basic stuff of the universe. Some physicists are playing with the idea that newfound particles, such as omega, may have complicated structures of their own. Some of the experts suspect that there may never be an end of this process of peeling onionlike skins from the mystery of matter. "This means," says Professor Luis W. Alvarez, who along with Dr. M. L. Stevenson made up the remainder of the omega hunting team, "that we scientists will never work ourselves out of a job."

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