At the International Conference on High Energy Physics in Brazil, the BESIII Collaboration report that, after 15 years of sustained research, it identified the dominant constituent of the X(2370) as a pseudoscalar glueball with spin-parity quantum numbers of 0⁻⁺
The strong interaction force tightly binds quarks inside protons and neutrons. Its mediator is called the gluon, just as the photon mediates the electromagnetic interaction. Notably, however, gluons can attract each other and form an entirely new particle—a bound state called a glueball.
The glueball is an important prediction of quantum chromodynamics, the theory that describes the strong interaction, and is also the only type of particle in nature composed entirely of force mediators. No particle of this kind has ever been observed experimentally, and its existence constitutes a crucial test of quantum chromodynamics.









