Tiny Discovery May Answer a Question About the Big Bang (New York Times)
Tiny Discovery May Answer a Question About the Big Bang
By James Glanz, New York Times
July 7, 2001
By observing millions of subatomic particles called B mesons, a team of scientists working at the Stanford Linear Accelerator Center in California has found new evidence of a basic but subtle lopsidedness in nature that may explain why the universe contains mostly matter, rather than being virtually empty and devoid of stars, planets and people.
The results found by a multinational team of about 600 physicists and engineers were announced today in Stanford.
The lopsidedness is "extraordinarily tiny," Dr. Jonathan Dorfan, the director of the center, said at a meeting of physicists here. Nonetheless, he said, it may explain "a spectacularly interesting phenomenon, namely why we are here."
The asymmetry was first seen in 1964 by Dr. Val Fitch of Princeton University and Dr. James Cronin of the University of Chicago in an experiment for which they later received a Nobel Prize.
The effect was revealed in slight differences in the behavior of a given type of particle — so-called kaons or neutral k's in the Fitch-Cronin experiment -- and its antimatter counterparts. Such differences may explain why the Big Bang explosion thought to have created the universe did not produce equal amounts of matter and antimatter, which then would have annihilated each other and left nothing but light.
But if matter and antimatter behaved differently in the cooling that followed the Big Bang, matter might have gradually begun to predominate in the universe. Physicists call these theorized differences charge-parity violation or CP violation.
But despite nearly 40 years of searching since the original experiment, physicists had been unable to show definitively that any other particles displayed CP violation. This left physicists to wonder whether the original discovery reflected some unexplained quirk or a basic natural law.
The new findings show with a statistical certainty of 99.997 percent that the effect also occurs in another type of particle, the B meson, the team says.
"People have looked for this or the equivalent under every rock" since the Fitch-Cronin experiment, said Dr. Stewart Smith, a Princeton physicist who is the spokesman for the team.
Dr. Fitch, who was not involved in the new work, agreed that — despite strong hints from earlier experiments at the Fermi National Accelerator Laboratory -- the new results are the first solid demonstration of CP violation in another particle.
The experiment produced millions of B mesons and their antimatter counterparts, anti-B mesons, and observed the rates at which they decayed into other particles. (Anti-B's are also called B-bars; the experiment is called BaBar, after the elephant in the children's books.)
Slight differences in the decay rates of the matter and antimatter particles established CP violation "with a very high probability," said Dr. Gautier Hamel de Monchenault, a physicist at the Atomic Energy Commission in Saclay, France, and the physics analysis coordinator of BaBar.
Dr. Hamel de Monchenault said the degree of CP violation observed seemed generally in line with what physicists expected in their standard model of particle physics, the framework that physicists use to describe the fundamental particles and forces in the universe.
A closely related experiment called Belle at the KEK accelerator laboratory in Tsukuba, Japan, is also measuring the effect with B mesons and, like BaBar, presented preliminary results last year. But last year, neither group could demonstrate an effect.
Despite the new results, most theorists agree that the degree of CP violation predicted by the standard model and observed in the new experiment is probably not enough to explain all the matter that is seen in the universe.
Dr. Natalie Roe, a BaBar collaborator at the Lawrence Berkeley National Laboratory, said at the meeting here that further experiments at the Stanford laboratory would both check the latest results and test the standard model's predictions in new ways.
"This is the beginning of the story," Dr. Roe said. "What we want to find is a crack in the standard model."