Neutrino

A neutrino is an electrically neutral elementary particle with tiny but nonzero mass. It interacts through the weak force and gravity, allowing it to pass through matter with little chance of collision.

Neutrino oscillation: The periodic change of a neutrino from one flavor to another as it propagates. Oscillation shows that neutrinos have mass and that flavor states mix.
Wolfgang Pauli: A theoretical physicist who proposed the neutrino in 1930 to explain missing energy in beta decay. His proposal introduced the particle before it could be detected.
Standard Model: The quantum field theory describing known elementary particles and three of their fundamental interactions. Neutrinos are among its elementary particles, though their masses require an extension or modification.
Solar neutrino: A neutrino produced by nuclear reactions in the Sun. Solar neutrinos test models of energy production in the Sun's core.
Neutrinoless double beta decay: A hypothetical nuclear decay that emits two electrons without emitting neutrinos. Its observation would establish lepton-number violation and support the Majorana-neutrino hypothesis.
Weak interaction: A fundamental interaction responsible for processes such as beta decay and neutrino scattering. Neutrinos interact through this force, which makes their collisions with matter rare.
Enrico Fermi: A physicist who developed the theory of beta decay and named the neutrino. His theory placed the neutrino in a quantitative account of weak decay.
Lepton: An elementary fermion that does not participate in the strong interaction. Neutrinos belong to the lepton family alongside charged particles such as electrons.
Supernova neutrino: A neutrino emitted during the collapse and explosion of a massive star. Most of a core-collapse supernova's released energy escapes as neutrinos.
Neutrino mass ordering: The unresolved question of whether the third neutrino mass state is heavier or lighter than the other two. Oscillation measurements determine mass-squared differences but leave the ordering uncertain.

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