Italy’s Gran Sasso lab sees muon–tau neutrino oscillation

Nature : Neutrinos come in three flavors: muon, electron, and tau. Scientists had proposed that neutrinos are able to oscillate, or change flavor, as they travel long distances through matter. But the phenomenon had only been observed for muon-to-electron oscillations until today. Now researchers with the OPERA collaboration at Italy’s Gran Sasso underground laboratory have confirmed that muon neutrinos can change to tau neutrinos. They detected several such oscillations in a muon neutrino beam shot 730 km from CERN in Switzerland to the lab. At Gran Sasso, the researchers used an automated system to look for tau leptons, which are produced when tau neutrinos strike the OPERA detector’s array of lead emulsion plates. Although the leptons show up only briefly as microscopic streaks, the researchers have managed to count a statistically significant number of them—five—between 2010 and 2015.