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Science File

Accelerator Findings Help Show Why There's Matter

August 07, 2004|Eric D. Tytell | Times Staff Writer

Researchers at the Stanford Linear Accelerator Center have observed a crucial difference between the behavior of matter and antimatter, providing insight into one of the key questions of physics: why there is matter in the universe.

Theoreticians agree that the Big Bang that created our universe produced equal amounts of matter and its exotic counterpart, antimatter. But the two are converted back into energy in a massive explosion when they come into contact.

For matter to have survived the universe's fiery beginning, it must have been preferentially retained while antimatter disintegrated. This unequal rate of destruction of matter and antimatter is called charge-parity violation, a term coined by Russian physicist Andrei Sakharov in 1967.

A large collaboration called BaBar is reporting this week that the accelerator results contain evidence of a strong charge-parity violation that may have retained matter after the birth of the universe.

The accelerator -- known colloquially as the B Factory -- flings electrons and their antimatter counterpart, positrons, together at high speeds, creating exotic particle pairs called B mesons and anti-B mesons, which immediately decay into a variety of different particles, producing, in almost every case, the same amount of matter and antimatter.

But after sifting through more than 200 million pairs of B and anti-B mesons, the team found 1,600 particles whose decay produced 13% more matter than antimatter, an asymmetry 300,000 times stronger than anything previously observed.

Even though the effect is rare, it still helps to explain why there was matter left over after the Big Bang, said physicist Fred Gilman of Carnegie Mellon University. "It only takes a little tiny difference overall to make it so that the universe now is made out of matter," he said.

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