Kamioka Observatory, ICRR (Inst. for Cosmic Ray Research), Univ. Tokyo
Why the Universe is filled with matter, rather than antimatter, is one of physics’ greatest mysteries. An experiment in Japan has now glimpsed a possible explanation: subatomic particles called neutrinos might behave differently in their matter and antimatter forms.
The disparity, announced at the International Conference on High Energy Physics (ICHEP) in Chicago, Illinois, on 6 August, may turn out not to be real: more data will need to be gathered to be sure. “You would probably bet that this difference exists in neutrinos, but it would be premature to state that we can see it,” says André de Gouvêa, a theoretical physicist at Northwestern University in Evanston, Illinois.
Even so, the announcement is likely to increase excitement over studies of neutrinos, the abundant but elusive particles that seem increasingly key to solving all kinds of puzzles in physics.
In the 1990s, neutrinos were found1, 2 to defy the predictions of physics’ standard model — a successful, but incomplete, description of nature — by virtue of possessing mass, rather than being entirely massless. Since then, neutrino experiments have sprouted up around the world, and researchers are realizing that they should look to these particles for new explanations in physics, says Keith Matera, a physicist on a US-based neutrino experiment called NOvA at the Fermi National Accelerator Laboratory (Fermilab) in Batavia, Illinois. “They are the crack in the standard model,” he says.
The excess of matter over antimatter in our Universe is extraordinary, because if the mirror-image particles were produced in equal quantities after the Big Bang, they would have annihilated each other on contact, leaving nothing but radiation. Physicists have observed differences in …