By Peter Weiss
As theorists see it, the universe exploded into being billions of years ago with equal parts matter and antimatter. Yet aside from traces produced in laboratories and detected in the atmosphere and space, nearly no antimatter exists now. Physicists at particle accelerators in California and Japan have now taken a step closer to understanding that puzzling absence.
New data from those accelerators, combined with older American results, raise to two the number of elementary particle types in which matter and antimatter have been observed to break down in different ways, scientists say.
Physicists discovered nearly 40 years ago that matter and antimatter versions of so-called K mesons decay slightly differently, a disparity called charge-parity, or CP, violation (SN: 3/6/99, p. 148). In the first moments of the universe, CP violation would have let matter survive at the expense of antimatter.
Two years ago, a team at the Fermi National Accelerator Laboratory (Fermilab) in Batavia, Ill., released results hinting that CP violation also occurs among particles called B mesons (SN: 2/20/99, p. 118). Since then, independent teams at the Stanford (Calif.) Linear Accelerator Center (SLAC) and at the KEK High Energy Accelerator Research Organization in Tsukuba, Japan, have been colliding tens of millions of electrons and their antimatter counterparts, positrons, looking for firm evidence of B meson CP violation (SN: 5/29/99, p. 342).
That evidence may now be in hand. This month, both groups released their latest figures for a parameter called sin 2(beta) or sin2(phi)1. It would equal 0 if there were no CP violation among B mesons.
The California team reports that sin2(beta) is 0.34 ± .20, whereas the team in Japan finds 0.58 ±.33. Averaging those results with Fermilab’s, scientists come up with a value of 0.49 ± .16.
“It appears that we have established now that there is CP violation in the B meson system,” says David G. Hitlin of the California Institute of Technology in Pasadena, a SLAC team leader. If upheld, that conclusion would bolster scientists’ hunch that CP violation is key to antimatter-matter disparity.
