Why This Particle's Decay Really Matters

CHICAGO--Scientists working at the giant Fermi National Accelerator Laboratory (Fermilab) particle accelerator nearby may have caught a long-sought second glimpse of a phenomenon that could explain one of the biggest puzzles in physics: Why the universe contains more matter than antimatter. According to long-held theories, the two types of particles should exist in equal amounts.

Physicists got their first hint that something was amiss in these theories more than 30 years ago, when experimenters studying the decay of particles called kaons were shocked to see an effect known as CP violation, a basic asymmetry between kaons and antikaons. The effect had not turned up in any other particle, however, so physicists have wondered whether CP violation is a general principle of nature or somehow restricted to a single system.

Now, Fermilab investigators may have spotted another case of CP violation in particles called B mesons in the form of a slight difference in the rate at which B mesons and anti-B mesons decay to a particular set of particles. Researchers studied the decays of about 200 B and anti-B mesons created in the debris of proton-antiproton collisions and saw B mesons decaying that way less frequently--but with a weak statistical confidence. "We're not claiming a detection," says Barry Wicklund of Argonne National Laboratory--just a hint of anomalous behavior.

The evidence is tantalizing but not conclusive, adds Al Goshaw of Duke University and co-spokesperson of the group that conducted the experiments, whose paper on the work is soon to appear in Physical Review Letters. "If it's there, we'll see it" with more data, he says.

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