Particles' odd behavior offers clue to matter's origin

Scientists find a mismatch between a particle- antiparticle pair. It may help explain emergence of matter.

As scientists piece together the history of the universe, they have had a hard time explaining why matter exists at all. By all rights, they say, the big bang should have been a big flash in the pan, yielding nothing tangible after the initial energy burst.

On Friday, though, an international team of physicists came a step closer to explaining matter's presence. Their latest key to unraveling the mystery: proof that a subatomic particle, called a B meson, can be subtly different from its antimatter counterpart.

This is the second family of particle- antiparticle pairs to exhibit the difference - an anomaly that may occur more widely than many had thought. The fact that the difference does exist - violating a property called charge parity (CP) - should help researchers explain why any matter at all emerged from the early universe.

"Now you can compare this phenomenon on two different systems. This allows you to point in the directions that will be most promising," says Stewart Smith, a Princeton University physicist and a spokesman for the team that made the discovery.

When a particle is generated, physicists say, so is its antiparticle. The two are like in mass, but their other properties are flip-flopped.

Yet each should perform in similar ways. In the world of antimatter, for example, the positron should perform the same way in an anti-atom as the electron does in an atom, thus showing charge parity.

Particles and antiparticles display another characteristic: When they meet, the pairs vanish in a burst of radiation. This, physicists say, presented the big-bang theory with a problem. Theorists had concluded that the big bang must have produced equal amounts of matter and antimatter. That meant that matter would have been annihilated as soon as it appeared. Yet from galaxies to grains of sand, they note, matter permeates the universe.

In the mid-1960s, however, physicists at the Brookhaven National Laboratory in New York discovered that, once in a great while, the antiparticle partner to a K meson decayed slightly faster than the K meson itself, violating charge parity.

The discovery prompted Soviet physicist Andrei Sahkarov to propose that, in a fraction of a billionth of a second following the big bang, CP violation could have handed matter the crown in a cosmic version of "Survivor."

When the dust settled, the cosmos ended up with "one part per billion of matter left over - that's us, no antimatter, and a whole lot of light," says Lawrence Sulak, chairman of the physics department at Boston University. "That can only have happened if the antiparticles decayed faster than the particles."

Yet for 37 years, K mesons and their antiparticles were the only members of the subatomic menagerie to exhibit CP violation, prompting some to wonder how broad the phenomenon really was.

Now, scientists working at the Stanford Linear Accelerator's "B Factory," in Palo Alto, Calif., have added another family to the list.

Their report is expected to be followed by one from Japan's National Laboratory for High Energy Physics, where the initial run of a similar B-meson-based experiment ended Friday. Those researchers say they expect to complete their calculations and report their results, perhaps as early as the end of this week.

The Stanford results are consistent with predictions about particle behavior offered by the Standard Model, an overarching framework in physics that describes the properties and functions of subatomic particles.

But, says Dr. Smith, "that's good news and bad news. It's great for the Standard Model. On the other hand, we know the Standard Model isn't complete, and yet-unknown physics is required to produce enough CP violation" to explain the big bang's aftermath.

(c) Copyright 2001. The Christian Science Monitor

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