Why is antimatter absent? Hunt heats up Scientists searching for the Achilles’

heel that wiped out antimatter have tak- en a big step, but they’re not yet certain where they’re headed.

The researchers want to know why the universe today appears to contain almost no antimatter, although presumably, in the Big Bang, both matter and antimatter formed in equal quantities.

Studies of the decay of particles and antiparticles known as B mesons promise vital clues. So, scientists in Japan and Cal- ifornia have built electron-positron collid- ers, called B factories, for making B mesons and exploring their breakdowns (SN: 5/29/99, p. 342).

Since the 1960s, physicists have known that physical laws occasionally operate slightly differently for matter than for antimatter, an asymmetry dubbed the charge-parity, or CP, violation. In the early universe, CP violation may have made some antiparticles disintegrate a little more readily than their matter counterparts, creating a tiny excess of matter. In this scenario, because matter and antimatter annihilate each other, nearly all antimatter would eventually vanish, leaving just enough matter to make up essentially everything in the universe today.

On Monday, at a meeting in Osaka, Japan, the B-factory teams unveiled their

Peering down a corridor of the KEK B factory.

first scientific results. Their findings indi- cate that they’re quickly closing in on a measurement of CP violation among B mesons. In the past year alone, each of the two machines has come up to speed and generated about 10 million B decays, the scientists reported. That’s as many as the formerly most prolific B-making machine, an accelerator at Cornell Uni- versity, produced in a decade.

“The performance has been extraordi- nary,” says David G. Hitlin of the Stanford (Calif.) Linear Accelerator Center (SLAC), site of the B factory in California. The Japanese machine’s team expects to have enough data “very soon” to better dis- cern the effect of CP violation on B mesons, adds Hirotaka Sugawara, direc- tor general of the KEK High Energy Accel- erator Research Organization in Tsukuba.

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At the 30th International Conference on High Energy Physics, the two teams pre- sented preliminary figures for a parame- ter known as sin2P or sin2cpl, which can have values between -1 and +1. Those ex- tremes represent maximum CP violation, whereas 0 implies none. Physicists don’t expect a negative result, which would mean that antimatter should have won the cosmic demolition derby.

Pinning down this parameter “is a high- stakes game,” Hitlin notes. After all, the result may challenge the prevailing stan- dard model of particle physics, which calls for sin 2p to be roughly 0.7.

In contrast, SLAC’s new value of sin2P, based on 120 events, is 0.12. With 98 events, the KEK group found 0.45. Last year, a group at Fermi National Accelera- tor Laboratory (Fermilab) in Batavia, Ill. , announced a value of 0.79, derived from 400 events (SN: 2120199, p. 118).

Given that all the sin2P figures so far are greater than 0, there’s “a reasonably high chance that we’ve already observed CP vi- olation in the B system,” comments Fermi- lab team member Joel G. Heinrich of the University of Pennsylvania in Philadelphia.

He and other B-meson specialists cau- tion, however, that large, overlapping un- certainties spread the three measure- ments over a wide range that includes 0. So, researchers can’t yet determine how much, if any, CP violation occurs.

An ultimate answer of 0, which the new SLAC result falls near, would be “stagger- ing,” says SLAC director Jonathan M. Dor- fan. It would have “major implications” for why the known universe is here, he adds. He predicts the SLAC team will nail down “a more precise number” by yearend.

Planned upgrades to both B factories may boost their collision rates more than fivefold. A retrofit of the Fermilab ma- chine is expected to up its rate by a fac- tor of 20, Heinrich says. -P Weiss

Team corners culprit in sudden oak death After 5 years of mystery, California

pathologists announced Monday that they may have found the cause of a new disease that makes oak trees ooze red liquid and then die.

The disease, sudden oak death, seems to come from a previously unknown species of the microscopic, funguslike Phytophthora genus, says David Rizzo, a plant pathologist at the University of Cal- ifornia, Davis. He and other members of the University of California oak-research team presented their findings at one of their study sites in Marin County.

So far, three species common in coastal woodlands have proved vulnerable: tan oak (Lithocarpus densiflorus), coast live oak (Quercus agrifolia), and black oak (Quercus kellogii) .

Thousands of trees, ranging from Santa Barbara into Humboldt County in north- ern California, show symptoms of the dis- ease. “What we’re worried about is that it will move,” Rizzo warns. The team hasn’t yet figured out how the disease spreads but urges people not to carry firewood or soil out of the affected region.

Rizzo’s nightmare scenario starts with campers on a visit to an infected coastal region collecting firewood from the abun- dant dead oaks. The party, with its left- over firewood, then travels to Yosemite and infects the park’s “gorgeous groves of black oaks,” Rizzo says.

That fear spurred the researchers to announce their preliminary results. Like those who study human disease, plant pathologists test suspect pathogens with procedures based on Koch’s postulates, named after a 19thcentury microbiolo- gist. First, the researchers collect a s u p posed infectious agent from a diseased subject. Then, they see whether it in-

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duces the disease in a healthy test sub- ject. If so, they finally check for the agent in the new victim.

So far, Rizzo’s team has successfully isolated Phytophthora from sick trees and introduced it into healthy plants. In about 3 months, the researchers expect to know whether sudden oak death results.

The Phytophthora sounds like a solid suspect to Frank H. Tainter of Clemson University in South Carolina. He’s nailed a relative, Phytophthora cinnamomi, as the cause of oak die-offs in Mexico. “The first time I saw an aerial photograph of the California oaks, in USA Today, I called [the California researchers] and said, ‘It looks a lot like Phytophthora.”’

A previously unknown Phytophthora lurking in woodlands also sounds plausi- ble to one of the authorities on these pathogens-Everett Hansen of Oregon State University in Corvallis. “Forests haven’t been studied that well,” observes Hansen, who’s describing five new species of Phytophthora.

The previously known species of the genus have been bad enough, notes George W. Hudler, a tree pathologist at Cornell University. One species caused the Irish potato famine of 1845, and an- other is attacking Port Orford cedars in the Pacific Northwest. P cinnamomi is killing thousands of acres of eucalyptus trees in Australia, says Hudler.

The newest scourge could have lived peaceably elsewhere, causing little dam- age until it came upon US. oaks, Rizzo speculates. Or perhaps some environmen- tal factor permitted a longstanding, low- level nuisance to become a rampant tree killer. Or the microbe itself may have turned virulent. At the moment, Rizzo, laments, he just doesn’t know. -S. Milius

AUGUST 5,2000