Detector catches neutrino flavor oscillation in action

Guardian : Neutrinos, which come in three different flavors—muon, electron, and tau—are notoriously hard to detect because they oscillate between the flavors as they travel. Although that oscillation behavior had never been seen directly, it was predicted by scientists who observed fewer muon neutrinos than expected. Most detectors use cosmic rays as the neutrino source, but Japan’s T2K experiment fires an artificial beam of muon neutrinos through Earth’s crust toward the Super-Kamiokande neutrino detector, 295 km away. Because researchers could control the energy of the initial muon neutrinos, they hoped to have a better chance of detecting the electron and tau neutrinos that would be produced. The results of the experiment, presented at a meeting of the European Physical Society, revealed a 7.5-sigma signal of evidence for electron neutrinos, the first direct proof of neutrino flavor oscillation.