Neutrino oscillation

Neutrino oscillation is the periodic change in a neutrino’s flavor as it propagates, arising because flavor states mix different mass eigenstates with unequal masses.

Neutrino mixing: The quantum-mechanical relation that expresses neutrino flavor states as combinations of mass eigenstates. The mixing matrix sets the amplitudes for flavor change during propagation.
Neutrino: A neutral, extremely light elementary particle that interacts through the weak force and gravity. Oscillation is a property of neutrinos produced and detected through weak interactions.
Super-Kamiokande: A large water Cherenkov detector in Japan that studies neutrinos and other rare events. Its atmospheric-neutrino data showed a zenith-angle-dependent deficit of muon neutrinos.
Neutrino mass ordering: The unresolved question of whether the third neutrino mass eigenstate is heavier or lighter than the first two. Matter-enhanced oscillations can distinguish the normal and inverted orderings.
PMNS matrix: The unitary matrix connecting neutrino flavor eigenstates with neutrino mass eigenstates. Its angles and phase determine the strength and pattern of oscillations.
Neutrino flavor: The electron, muon, or tau identity assigned to a neutrino through its weak interactions. Experiments observe flavor at production and detection, rather than mass directly.
Sudbury Neutrino Observatory: A Canadian heavy-water detector that measured solar neutrinos through charged-current, neutral-current, and elastic-scattering reactions. Its neutral-current measurement showed solar electron neutrinos changed into other active flavors.
Leptonic CP violation: A difference between certain processes involving leptons and their charge-conjugate counterparts. Flavor-transition asymmetries could reveal the CP-violating phase in the PMNS matrix.
Neutrino mass eigenstates: The neutrino states with definite masses that propagate with distinct quantum phases. Their unequal masses make their phases diverge as they travel.
Quantum superposition: A quantum state formed as a coherent combination of multiple possible states. A flavor state is a superposition of mass states that evolve differently.

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