Any of a group of subatomic particles having odd half-integral spin (, ). Fermions are named for the Fermi-Dirac statistics that describe their behaviour. They include particles in the class of leptons, baryons, and nuclei of odd mass number (e.g., tritium, helium-3, uranium-233). They obey the Pauli exclusion principle. Fermions are produced and undergo annihilation in particle-antiparticle pairs. See also boson.
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