The Sciences

New Evidence for Flavor-Switching Neutrinos

An accelerator experiment confirms that neutrinos can mysteriously morph from one type to another.

By Gregory MoneJan 23, 2014 1:00 PM
Super-Kamiokande04.jpg
The super-kamiokande detector helped refine scientists’ understanding of matter. | Kamioka Observatory, ICRR (Institute for Cosmic Ray Research), The University of Tokyo

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About 15 years ago, physicists discovered that the neutrino, a subatomic particle, seems to be able to switch from one type, or flavor, to another while in flight. 

Last year, an international coalition called the Tokai to Kamioka (T2K) collaboration produced new evidence for this strange phenomenon, which may lead to insights about why there is more matter than antimatter in the universe.

Neutrinos come in three flavors: electron, muon and tau. All of them interact with other matter in different ways. In the experiment, researchers in Tokai, Japan, used a particle accelerator to shoot beams of muon neutrinos to the Super-Kamiokande detector some 185 miles away. 

En route, some muon neutrinos transformed into electron neutrinos. “It’s like throwing vanilla ice cream a long distance and seeing some of it turn into chocolate,” says physicist Chang Kee Jung of New York’s Stony Brook University. 

To see if antimatter behaves the same way, the scientists will measure how likely anti-muon neutrinos are to turn into anti-electron neutrinos. If neutrinos are more likely to transition from one matter state to another, rather than one antimatter state to another, then the primordial neutrinos in the early universe were probably also more likely to become matter rather than antimatter. 

The result: a cosmos made up of something rather than nothing.

[This article originally appeared in print as "Particle Finds a New Identity."]

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