Neutrinos are elementary particles that are fundamental building blocks of nature.  Neutrinos come in three types - muon, electron and tau - generally travel at the speed of light and can easily pass pass through ordinary matter, like Earth's crust.

Researchers with the Tokai to Kamioka experiment (T2K) at the Japan Proton Accelerator Research Complex have discovered that muon neutrinos can spontaneously change their "flavor" to electron neutrinos. Scientists had previously measured the change of muon neutrinos to tau neutrinos and electron neutrinos to muon neutrinos or tau neutrinos, she said. 

The shift of muon neutrinos to electron neutrinos detected in the new experiment is a new type of neutron oscillation that opens the way the way for new studies of a matter-antimatter symmetry called charge-parity, or CP violation.

"This CP violation phenomenon has not yet been observed in a neutrino, but may be the reason that our universe today is made up mostly of matter and not antimatter," said CU-Boulder Assistant Professor Alysia Marino of the physics department, part of a university contingent that participated in the experiment. 

Why matter trumped antimatter - muon neutrinos can change 'flavors' to electron? - Science Codex