Siding with Symmetry

All summer long the world of physics has suffered from scientific confusion--all because experimenters from Columbia University and the State University of New York announced that they had demonstrated that nature's laws of symmetry are not inviolate. Now, less than three months later, order has apparently been restored. At a conference in Berkeley last week, scientists from the European Organization for Nuclear Research (CERN) sided with symmetry. Their own more comprehensive experiment, they said, showed no evidence of a violation of symmetry.

Center of the scientific storm is a subatomic particle called the eta meson, which lives for only a billionth of a billionth of a second before breaking down into three smaller particles called pions--one positive, one negative, one without any electrical charge. According to the laws of symmetry, the positive and negative pions should have identical energies. But when a team led by Columbia University's Dr. Paolo Franzini examined 1,441 photographs of eta-meson decay in the Brookhaven bubble chamber (TIME, July 8), they found that in 53% of the photographs the positive pion apparently had more energy than its negative counterpart--a significant violation of symmetry.

Reversing the Field. In their experiment at Geneva, the European physicists also studied eta-meson decay. They analyzed 10,665 photographs of tracks made by pions in the CERN spark chamber, and in their larger, more reliable statistical sample, they found no significant difference in the energy levels of positive and negative pions.

Because the Brookhaven bubble chamber has a fixed magnetic field, the positive pions that Franzini studied always curved in one direction, while the negative pions went the other way. If the field had been uneven for any reason, the higher positive-pion energy levels detected at Brookhaven might well have been erroneous. In the CERN spark chamber, the magnetic field was periodically reversed to make sure that positive and negative pions would both be subject to any variations in the field.

Though most scientists at the Berkeley meeting privately sided with the CERN findings, none would state flatly that symmetry had, after all, been restored. Franzini's group is preparing a new round of experiments at Brookhaven in an attempt to confirm the violations they reported; still another team led by Columbia University Physicist Leon Lederman will attempt a similar experiment, and the CERN scientists plan to make more tests of their own. "The evidence from the CERN experiments is by no means conclusive," says Franzini defiantly. "Many more experiments are needed before we can say who is right."

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