Neutrino oscillations are a quantum phenomenon in which neutrinos change their type, or “flavor,”—electron, muon, or tau—as they travel through space. This surprising behavior implies that neutrinos must have mass, contrary to the original predictions of the Standard Model of particle physics.
Neutrinos are produced in a specific flavor during processes like nuclear reactions in the Sun or in particle accelerators. However, experiments have shown that as neutrinos travel, they can transform from one flavor to another. This transformation, or oscillation, occurs because the flavor states are quantum mixtures of neutrino mass states, and each mass state travels slightly differently through space.
The discovery of neutrino oscillations was confirmed by experiments such as Super-Kamiokande in Japan and SNO (Sudbury Neutrino Observatory) in Canada. These results were groundbreaking, proving that neutrinos are not massless and leading to a major revision of the Standard Model.
Neutrino oscillations have profound implications for our understanding of particle physics, the early universe, and the fundamental nature of mass. They also open the door to new physics beyond the Standard Model, possibly connected to the origin of matter in the universe.