A Step Away from Symmetry

The experiment involved infinitesimal particles of matter so slight and evanescent that they survived only a billionth of a billionth of a second. In their place they left still lighter particles that made fine lines across a bubble chamber at Brookhaven National Laboratory. And in those curving tracks scientists traced the possibility of trouble for vast and sweeping theories that involve not only tracks in bubble chambers and bits of atoms, but also distant stars and still undiscovered galaxies.

The Brookhaven experiment involved a fast-decaying subatomic particle known as an eta meson, which breaks down into three lighter particles known as pions--one with no electrical charge. According to the theory of symmetry, the positive and negative pions should not have shown any significant difference in speed. But 53% of the time, the positive pion zipped across the bubble chamber with more energy than its negative antiparticle.

Chaos & Shock. The difference might seem negligible, but scientists have speculated for years on the fascinating possibility that for every bit of matter, there is an equal and opposite bit of antimatter somewhere in the universe. In the world of antimatter, all particles would be the exact mirror image of their material selves, except that their electrical charges and magnetic poles would be reversed. And it was this that the experiment at Brookhaven called into question. For if it had been done in an antimatter world, the faster positive pion would have been negatively charged. The theoretical symmetry of matter and antimatter would not hold.

Science writers outdid themselves reporting that all physics was in a state of chaos and shock. But the real shock came almost a decade ago when Professors Tsung Dao Lee of Columbia and Chen Ning Yang of the Institute for Advanced Study in Princeton challenged the concept of "parity" and the idea of symmetry in matter and antimatter for so-called "weak" forces in nature. What was needed was an experiment to check out possible violations of physical symmetry in stronger forces.

This was just what Columbia's Dr. Paolo Franzini had in mind when he went to work with Brookhaven's synchrotron in January 1965. Along with his wife, Dr. Juliet Lee-Franzini, Drs. Charles Baltay and Lawrence Kirsch, he fired particles called pi mesons into a bubble chamber filled with liquid deuterium. About one-thirtieth of the times that a pi meson hit a deuterium nucleus, out came the eta meson, which decays into three pions. The pions streaked through the bubble chamber, the positive leaving a line that curved to the right, the negative peeling off to the left, and the neutral leaving no path at all. After analyzing photographs of 1,441 sets of such tracks, the Franzinis determined that in more than half of the cases the positively charged pion was therefore traveling faster than its negative counterpart.

A New Force? Despite the ballyhoo of the announcement, other physicists, including J. Robert Oppenheimer, weighed in with warnings against hasty interpretation of the new data. Columbia's Lee has himself suggested that some unidentified force might produce such discrepancies. Still, in the abstruse world of nuclear physics, the results remain impressive. Columbia's Samuel Devons nostalgically declared, "Before we had a beautiful theory, nice and symmetrical." But he added a hopeful note: "The exceptions may be telling us something."

One thing they may be saying is that the forces which bind electrons to nuclei in the world of matter are not symmetrical. As for the oft-debated topic of antiworlds and anti-galaxies, the Franzinis prefer to leave this to the cosmologists. But their eta-meson project does move a tiny step closer to the possibility of clarifying the differences between a particle and its antiparticle.

This file is automatically generated by a robot program, so reader's discretion is required.