Washington

The standard model of high-energy physics received a ringing endorsement last week, as researchers revealed the most accurate measurements so far taken of an effect that may explain the surplus of matter in the Universe.

The results, presented at the International Conference on High Energy Physics in Amsterdam by teams from the United States and Japan, focus on a fundamental effect that some think could explain why we exist.

Physicists believe that at the time of the Big Bang, the Universe contained equal amounts of matter and antimatter. But these should have annihilated each other, leaving no matter to create galaxies, stars — or us. One explanation for the glut of matter in the Universe is an effect called charge–parity (CP) violation, which causes matter and antimatter to behave in slightly different ways.

Two groups — the Belle collaboration based at the High Energy Accelerator Research Organization in Tsukuba, Japan, and BaBar at the Stanford Linear Accelerator Center in the United States — have measured the decay of particles called B mesons and their antiparticle equivalent, anti-B mesons. Both teams detected a slight difference in the decay rates of the particles, which is interpreted as evidence for CP violation.

Data on particle decays (right) obtained using BaBar's equipment vindicate physics' standard model. Credit: SLAC

The measurements, which are around twice as accurate as those previously taken (see Nature 412, 105; 200110.1038/35084338), agree well with each other and also with the standard model's predictions. “The agreement is as perfect as it could be,” says Stewart Smith, a physicist at Princeton University and spokesman for the BaBar collaboration.

Despite this support for the standard model, current measures of CP violation show that the effect is not strong enough to account for the excess of matter. “The measurement fails by a factor of ten billion or so,” Smith says. “There's something out there that we don't know about yet. These latest measurements don't even give a hint.”

Some physicists believe that a possible explanation could be the existence of super-heavy particles that are not predicted by the standard model. The presence of these particles in the early Universe would have influenced the balance between matter and antimatter, tipping the scales in the favour of matter.

Delegates in Amsterdam were due to hear tentative evidence for super-heavy particles this week. The g-2 experiment at the Brookhaven National Laboratory in New York state measures a property of particles called muons that should deviate slightly from the predictions of the standard model if super-heavy particles do indeed exist. The latest results from Brookhaven hint at this deviation, but physicists will treat the results with care after a similar announcement last year turned out to be based on a flawed calculation (see Nature 410, 291; 2001 and Nature 415, 6; 2002).