Washington

Researchers at the Stanford Linear Accelerator Center (SLAC) in California have confirmed an important tenet of the standard model of high-energy physics. They have successfully measured a parameter that may help to explain the preponderance of matter over antimatter in the Universe.

An international team of 600 physicists announced on 6 July that they had measured the parameter, which expresses the degree of asymmetry between heavy subatomic particles called B mesons and their corresponding anti-B mesons.

The long-awaited finding, based on the observation of 32 million decay events by a 1,200-tonne detector called BaBar, confirms the existence of the overall asymmetry, known as charge-parity (CP) violation.

“We're absolutely delighted,” says Stewart Smith, a physicist at Princeton University and spokesman for the experiment. “We expected it would take another year to get this far.”

The 'B Factory' experiment, which generated the result, was devised and built by a team led by Jonathan Dorfan, who is now director of SLAC (see Nature 403, 586; 2000).

A rival international team at the KEK particle physics laboratory in Japan is set to announce its own measurement of CP violation at a news conference next week.