Gluonid

Gluonid is a term that appears in some theoretical discussions to denote a hadronic state whose structure is dominated by gluons. In mainstream quantum chromodynamics the established concept for such states is a glueball, a color-singlet bound state of gluons with no valence quarks. The word gluonid, formed from “gluon” and the -id suffix meaning “resembling,” is sometimes used to describe a gluon-rich excitation or to distinguish purely gluonic states from hybrids that incorporate quarks.

From a theoretical standpoint, gluonids would arise because gluons, unlike photons, carry color charge and can self-interact. Lattice QCD studies predict several glueball candidates with specific quantum numbers, such as scalar and tensor states, though precise identifications remain unsettled. A gluonid would be expected to exhibit properties reflecting strong gluonic content, potentially including distinctive decay patterns into meson final states and relatively weak coupling to photons.

Experimentally, no unambiguous gluonid has been established, and the term is not part of the standard nomenclature. Resonances observed in the 1.5 to 1.7 GeV region, including certain f0 states, have been discussed as possible glueball candidates or as mixtures with quark-antiquark mesons rather than a clearly defined “gluonid.” The status remains speculative, and researchers continue to search for definitive evidence of purely gluonic hadrons.

See also: glueball, hybrid meson, quantum chromodynamics.