Partons (internal constituents of hadrons) observed in deep inelastic scattering experiments between protons and electrons at SLAC; this was eventually associated with the quark model (predicted by Murray Gell-Mann and George Zweig in 1964) and thus constitutes the discovery of the up quark, down quark, and strange quark. 1974

The charm quark, charmed quark or c quark (from its symbol, c) is the third most massive of all quarks, a type of elementary particle.Charm quarks are found in hadrons, which are subatomic particles made of quarks. Examples of hadrons containing charm quarks include the J/ψ meson ( J/ψ), D mesons ( D), charmed Sigma baryons ( Σ c), and other charmed particles.