Physicists with the BES III experiment have uncovered convincing new evidence of glueballs, composite particles made entirely of gluons predicted by quantum theory. The results appeared in a preprint on arXiv last month and were presented at the International Conference on High Energy Physics (ICHEP).\n\nAll matter is made of quarks held together by gluons, carriers of the strong nuclear force. The Higgs boson, discovered in 2012, was the final missing piece of the Standard Model, but glueballs remain unconfirmed.

They are a direct prediction of quantum chromodynamics, the theory of the strong force. As Matthew Francis wrote in 2015, glueballs are part of why matter has mass, alongside the Higgs.\n\nGluons stick to each other, not just quarks, meaning a particle made purely of gluons should be possible. The J/ψ particle (discovered in 1974), a charm quark–antiquark meson, decays producing many gluons and hadrons, making it ideal for glueball searches.

According to astrophysicist Ethan Siegel, a glueball must have zero spin, no electric charge, and odd parity, among other properties.