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A hadron is a strongly interacting composite particle described by quantum chromodynamics. Familiar hadrons contain quarks and gluons in an overall color-neutral state. The proton and neutron are baryons; the pion is a meson.
The quark model labels ordinary hadrons by their valence content, but this does not list every dynamical constituent. Gluons and additional quark–antiquark contributions affect masses and interactions. Distinguishing a composite hadron from an elementary particle is useful when comparing low-energy models with scattering experiments that resolve internal structure.
