quarkgluon

Quarkgluon (often used to refer to the quark-gluon plasma in the context of quantum chromodynamics) denotes a state of matter in which quarks and gluons, ordinarily confined within hadrons, become deconfined and form a strongly interacting medium. This deconfined phase is predicted by quantum chromodynamics (QCD) and is believed to have existed microseconds after the Big Bang and may be recreated momentarily in heavy-ion collisions.

In the quark-gluon plasma, color charges move freely over distances larger than hadron sizes. The medium behaves like a nearly perfect liquid with a small shear viscosity to entropy density ratio. Its thermodynamic properties are studied using lattice QCD; the transition from hadronic matter to a deconfined phase at small baryon density is generally described as a crossover around a critical temperature near 150–160 MeV. At higher baryon density, a more complex phase diagram with possible critical points is explored.

Experiments at the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC) have produced hot, dense matter with signatures associated with deconfinement, including jet quenching, strong collective flow, and enhanced production of strange hadrons. Direct photons and dileptons provide information about the early stages of the medium. Measurements help constrain the equation of state and transport properties.

Although "quarkgluon" is occasionally used as a shorthand in discussions of the deconfined phase, the standard term in the literature is quark-gluon plasma. The field continues to investigate the properties, evolution, and phase structure of this extreme state of matter, with implications for cosmology and the behavior of dense nuclear matter.