gluonium

Gluonium, also known as a glueball, is a hypothetical type of meson that consists of gluons. Mesons are composite particles made up of a quark and an antiquark. However, gluonium would be composed entirely of gluons, which are the force carriers of the strong nuclear force. The existence of gluonium is predicted by quantum chromodynamics (QCD), the theory of the strong interaction. QCD allows for the possibility of glue-rich states that are not bound states of quarks and antiquarks. These gluonic states are called glueballs or gluonium.

Identifying gluonium experimentally has proven to be a significant challenge. Glueballs are expected to have different properties than ordinary quark-antiquark mesons, such as different decay patterns and masses. However, the spectrum of known mesons is complex, and distinguishing a pure glueball from other mesonic states can be difficult. Several candidate states have been proposed over the years, but none have been definitively identified as gluonium. Searches for gluonium continue in particle physics experiments, often by looking for unusual production or decay modes that would be characteristic of a gluon-only composite.