Neutrino Oscillations Reveal Neutrino Mass
Neutrinos come in three flavors. Electron neutrinos appear in beta decay. Muon neutrinos emerge from pion decay. Tau neutrinos show up in high-energy processes.
However, neutrinos change flavors during travel. This phenomenon is called neutrino oscillation. Experiments detect fewer neutrinos than expected. Solar neutrinos arrive reduced. Atmospheric neutrinos disappear over distance.
Oscillations prove neutrinos have mass. Massless particles travel at light speed. They stay in one flavor forever. Yet differences in mass squares drive mixing.
Flavor states mix into mass eigenstates. Three mass states exist: ν₁, ν₂, ν₃. Each carries a tiny mass. Propagation happens in mass states. Interference creates oscillations.
The probability oscillates with distance. It depends on energy and mass differences. Larger Δm² causes faster changes.
Two main mass splittings dominate. Δm²₂₁ affects solar neutrinos. Δm²₃₂ influences atmospheric ones. Experiments measure these precisely.
The mass ordering remains open. Normal hierarchy places m₃ heaviest. Inverted hierarchy puts m₃ lightest. Future data from JUNO or DUNE may resolve it.
Neutrino masses stay very small. Upper limits sit below 0.1 eV. They exceed zero clearly. This breaks the Standard Model slightly.