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Physicists find difference between matter, antimatter

Associated Press reporter Matthew Fordahl filed this interesting story about the research and study by physicists on the behavior of matter and antimatter.

Stanford, California - Physicists have taken some of the most precise measurements so far of the behavior of matter and antimatter, and their findings could help explain why the universe is filled with something rather than nothing.

Researchers have long known that during the Big Bang 13 billion years ago, equal amounts of matter and antimatter were created.

And researchers also know that when these two forms of matter collide, they annihilate each other.

But there is almost no antimatter in the universe today. This raises a question that has fascinated and perplexed physicists: Why is the universe still filled with matter---stars, planets and people? Why isn't the cosmos a complete void?

Physicists have tried to answer the question by reproducing antimatter in linear accelerators, then comparing its behavior --- its rate of decay --- to that of regular matter.

In a paper submitted July 6, 2001 for publication in Physical Review Letters, an international team of physicists working at Stanford University announced they have found differences in the decay rates of so-called "B" meson sub-atomic particles and their antimatter counterparts.

That could help explain why matter rather than anti-matter dominates the universe today.

"B" mesons and anti-"B" mesons, which are created for a trillionth of a second by high speed particle collisions in accelerators, are actually the second subatomic particle in which researchers detected a difference in the decay rate, known as a charged-parity violation.

The phenomenon was first detected in 1964, while researchers were studying the kaon, or "K" meson, and its antimatter equivalent. Those researchers, based at Brookhaven National Laboratory in New York won the Nobel Prize for their work.

"After 37 years of searching for further examples of CP violation, physicists now know that there are at least two kinds of subatomic particles that exhibit this puzzling phenomenon," said Stewart Smith, a Princeton University physicist and member of the international team.

Physicists seeking CP violations measure their results on a scale from zero to plus or minus one. The work done at the Stanford accelerator is significant because the result is not zero, which would mean the rate of decay are the same.

"This is the first result that has come out that is convincingly different from zero, which is a very important result," said Val Fitch, who shared the Nobel in 1980 for the 1964 kaon discovery.

The paper released Friday is not the first to show CP violation in the "B" meson particles. A team in Japan released similar results, though their measurements have not been as precise.

Smith and more than 600 scientists and engineers from 73 research institutions around the world have done this research using BaBar, a 1,200-ton "B" meson detector at the Stanford Linear Accelerator Center.