= Quantum chromodynamics
{title2=QCD}
{wiki}
= QCD
{c}
{synonym}
Quantum chromodynamics, or QCD, is the non-Abelian $SU(3)_c$ <gauge theory> of <quarks> and <gluons>. Quarks transform in the fundamental color representation and the eight gluon fields in the adjoint representation. The non-Abelian field strength generates gluon self-interactions as well as quark–gluon interactions.
The <strong coupling constant> changes with scale: it becomes small at sufficiently high energies, permitting perturbative predictions, and grows toward the <QCD scale>. Low-energy color confinement and hadron structure are therefore not obtained by extrapolating a few weak-coupling diagrams without qualification. <Parton distribution functions> describe the long-distance input needed for many hard hadron-scattering predictions. <Jets> connect the calculated energetic partons with measured sprays of color-neutral particles after <hadronization>.
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