What are glueballs?

Why in News?

At the International Conference on High Energy Physics in Brazil, the international Beijing Spectrometer (BESIII) Experiment collaboration announced that it had established a complete experimental evidence chain supporting the existence of a glueball. A glueball is a hypothetical composite particle made entirely of gluons, the force-carrying particles of the strong nuclear force.

Key Points

A glueball is a composite particle predicted by Quantum Chromodynamics (QCD) that would be composed entirely of gluons, without quarks or other matter particles as its constituents.

Nature has four fundamental forces: gravity, the strong nuclear force, the weak nuclear force and electromagnetism. The strong force holds quarks together inside protons and neutrons and also contributes to binding atomic nuclei.

Quantum Chromodynamics (QCD) is the theory that describes the strong interaction. In QCD, the strong force is mediated by particles called gluons, just as the electromagnetic force is mediated by photons.

Unlike photons, however, gluons carry colour charge and can interact with one another. This unique property of gluons allows them, according to QCD, to bind together and form composite particles known as glueballs.

Glueballs were theoretically predicted in the early 1970s, but providing conclusive experimental evidence for them has remained a major challenge in modern particle physics.

The BESIII collaboration reached its latest result after around 15 years of research involving scientists from 15 countries. Researchers analysed billions of measurements produced at an underground particle collider in western Beijing.

Glueballs are particularly difficult to identify because they can have properties similar to those of ordinary particles made from quarks. Moreover, QCD predicts that glueballs can exist in different forms or quantum states.

Connection with the Standard Model

According to the Standard Model of particle physics, atomic nuclei contain protons and neutrons, while protons and neutrons themselves are composed of quarks. Gluons mediate the strong interaction that binds these quarks together.

Source: PHYS

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