Physicists put a value that matters on the standard model

Experimental physicists have derived a more definitive value for the parameter that explains the surplus of matter over antimatter when the Universe began. But the result has left theorists with some explaining to do.

At a 10 May seminar at CERN, the European Laboratory for Particle Physics in Geneva, the researchers announced that they had obtained measurements that further confirmed the existence of 'charge–parity (CP) violation' — the phenomenon predicted by the standard model of particle physics to be behind the existence of matter in the Universe.

The CERN team reported a value of 15.3 ± 2.6 × 10⁻⁴ for the parameter linked to CP violation. “These errors are considerably smaller than any reported before,” says Frank Wilczek, a theoretical physicist from the Massachusetts Institute of Technology.

But theoretical calculations forecast a larger range of values for the parameter of between 4.2 × 10⁻⁴ and 13.7 × 10⁻⁴ (see Nature 402, 22–23; 1999). “It is hard to say whether these new results are consistent with the standard model,” Wilczek says. “The torch has now been passed on to the theoretical side.”