February 2, 2012
The BaBar collaboration’s detailed studies of the subtle ways in which matter behaves differently from antimatter are hailed as one of the success stories of experimental high-energy physics. After all, BaBar data and measurements have confirmed a nearly 40-year-old theory that explained the asymmetry between matter and antimatter, and helped convince the Nobel Prize committee to award the 2008 Nobel Prize in Physics to Makoto Kobayashi and Toshihide Maskawa, the two Japanese developers of that theory.
But BaBar’s SLAC-based search for matter-antimatter asymmetries did not end there. Perhaps Kobayashi's and Maskawa's theory, which is now part of the Standard Model of particles and interactions, is not the whole story.
"We know our current picture of particle physics, the Standard Model, cannot be complete, as it vastly underestimates the universe’s matter-antimatter asymmetry," said Aaron Roodman of SLAC and Stanford's Kavli Institute for Particle Astrophysics and Cosmology. "Some new source of asymmetry in particle interactions or decays must exist."
In a collaboration paper headed to the journal Physical Review D, Roodman, his graduate student Brian Lindquist and SLAC Staff Scientist Mathew Graham search for one such possible new source by studying an asymmetry in a particular decay of charged B mesons. B mesons decay in literally thousands of different ways, but about 40 times in a million the charged B decays into three charged K mesons. The theoretical expectation, based on Kobayashi’s and Maskawa’s very successful theory, is that the positively charged B+ will undergo this decay about as frequently as the negatively charged B– meson.
But BaBar found that the numbers of these decays did not exactly balance. The negative B– decayed into three charged K mesons 30 percent more often than the positive B+ did. This asymmetry differs from zero by only 2.8 sigma, "not enough to claim a discovery, but perhaps a tantalizing hint of something new," Lindquist said.
"All of the data collected by BaBar have been analyzed in this measurement," Roodman said, "but I expect that our colleagues at BELLE and at the LHCb experiment will be able to shed further light on our result."