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Physicists announce progress on question of missing antimatter

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TOKYO — Why is the world filled with something rather than nothing?

In what could evolve into the answer to one of physics' most basic questions, scientists this week laid out the first steps in their search for a difference between matter and antimatter.

Two international teams of scientists made the announcement at a conference in Japan, and while their findings are very imprecise, experts say the research's direction is highly promising.

Gerry Bauer, a Massachusetts Institute of Technology researcher who also studies matter, called the experiments a milestone in a road that began with a 1964 study that won the Nobel Prize.

The research challenges the predictions of the Standard Model, a set of mathematical formulas physicists use to describe the universe's elementary particles and their interactions. Disproving the Standard Model would open the way for alternative models of the universe.

If anyone can find a way to contradict the Standard Model, Bauer said, "Then everyone's very excited."

"What we're trying to do is understand the most fundamental building blocks of the universe," David Hitlin, spokesman for one of the two projects, called BaBar, said after the researchers gave a progress report Monday at the 30th International Conference on High Energy Physics in Osaka, Japan. "Over time, you develop a true understanding of how the universe is composed, how it developed from the time of the Big Bang."

Theoretically, nature is symmetrical: Every known subatomic particle, the matter that makes up the world, is paired with an antiparticle of antimatter.

Early in the life of the universe there was slightly more matter than antimatter. Today, antimatter is found only in cosmic rays and particle accelerators.

So where did all that antimatter go?

If antimatter decays more quickly than matter, that could help answer the question. What the teams are doing is studying the decay rates in a particular particle to see if there is a difference that would allow for the universe to exist.

This confusing contradiction to the rule of particle-antiparticle symmetry is a phenomenon called "CP violation," or "charge-parity violation."

The physicists are studying specific particles — B mesons — in laboratories called "B Factories," where they are making millions of the subatomic particles.

Both teams said their data is very preliminary and "still very imprecise," said Hitlin, spokesman for the California-based BaBar. They mostly wanted to let their colleagues know that they had taken this important first step down the road.

If they find no difference in decay rates, that would contradict the Standard Model's prediction. So far, Belle's findings are very much in line with the Standard Model, BaBar's somewhat less so.

Asymmetry was first found in 1964 in another particle. In 1998 and 1999, researchers found signs of asymmetry in B mesons at the Fermi National Accelerator Laboratory outside Chicago.

Bauer, who worked on the 1998 project at Fermilab, said researchers have been "desperately trying" to find a conflict with the Standard Model because that would make room — conceptually — for the many alternative models of the universe that abound today, such as string theory.

String theory posits that all the particles that make up the world are actually tiny vibrating loops, resonating in concert.

The results of the research are good, but not yet statistically strong enough to make definitive statements, said Fumihiko Takasaki, spokesman for the second group, Belle. Belle is based at KEK, a Japanese national laboratory for high energy accelerator research in Tsukuba City, near Tokyo.

"It's a hint of CP violation in B meson decay," he said. "This is a very good start."

BaBar is based at the Stanford Linear Accelerator Center in California.

The Belle team aims to submit its findings to a scientific journal in October or November. The BaBar team will publish in six months or so.

On the Net: BaBar home page: www.slac.stanford.edu/BFROOT/index.html

KEK High Energy Accelerator Research Organization: www.kek.jp

Conference web site: ichep2000.hep.sci.osaka-u.ac.jp/