Gluonide

Gluonide is a hypothetical color-singlet bound state of gluons proposed in certain nonperturbative models of quantum chromodynamics. In these frameworks a gluonide represents a multi-gluon excitation that extends the concept of the glueball, incorporating configurations with two or more constituent gluons and distinct J^PC quantum numbers. The exact spectrum depends on the model, but lightest gluonides are typically expected to be in the GeV mass scale, with masses and widths sensitive to the strength of gluonic self-interaction and to mixing with quark-antiquark mesons.

In theory, gluonides would be produced in gluon-rich processes, such as high-energy hadron collisions or radiative decays of heavy quarkonia, and would decay primarily into pairs or multiplets of light mesons, though decays to photons or other gluonic channels are also considered.

Their experimental identification is challenging because gluonides can mix with conventional mesons with similar quantum numbers, and because their decay patterns can resemble those of ordinary resonances.

As of now, there is no experimental confirmation of a gluonide. Searches in collider data and in quarkonium decay spectra have not produced unambiguous signals, and predictions vary across models. The concept remains a speculative component of discussions on nonperturbative QCD and the full spectrum of gluonic excitations.

Etymology: the name combines 'gluon' with the -ide suffix used for bound states, signaling a multi-gluon bound system.