QCD matter

QCD matter is matter whose constituents and interactions are governed by quantum chromodynamics, including color-neutral hadrons and deconfined quark–gluon plasma.

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Quantum chromodynamics: The quantum field theory of quarks and gluons and their strong interactions. It is the fundamental theory governing QCD matter.
Color confinement: The phenomenon that prevents isolated color-charged particles from appearing as free particles at low energies. It keeps quarks and gluons bound inside ordinary hadrons.
Relativistic heavy-ion collision: A collision of heavy atomic nuclei at speeds close to the speed of light. Such collisions briefly create hot QCD matter for experimental study.
Hadronic matter: Matter whose relevant constituents are hadrons rather than deconfined quarks and gluons. It contrasts with quark–gluon plasma, though both are forms of QCD matter.
Quark: An elementary fermion that carries color charge and participates in the strong interaction. Quarks are constituents of hadrons and the mobile degrees of freedom in plasma.
Asymptotic freedom: The weakening of the strong interaction between quarks at very short distances or high energies. It helps explain why sufficiently hot QCD matter can behave as deconfined constituents.
Relativistic Heavy Ion Collider: A collider at Brookhaven National Laboratory that collides relativistic heavy ions and polarized protons. RHIC experiments investigate the properties of quark–gluon plasma.
Electromagnetic plasma: An ionized gas of charged particles whose collective behavior is governed mainly by electromagnetism. It offers a familiar plasma comparison, but QCD plasma carries color charge and is strongly coupled.
Gluon: A massless gauge boson that mediates the strong interaction and carries color charge. Gluons bind quarks in hadrons and contribute directly to plasma dynamics.
Quark–gluon plasma: A state of matter in which quarks and gluons are not confined within individual hadrons. It is the best-studied deconfined phase of QCD matter.