Physicists confirm ‘glueball,’ a particle made of pure force with no matter inside

After nearly 50 years of searching, an international team of physicists has presented what they describe as the clearest evidence yet for the existence of a glueball — an exotic particle composed entirely of force-carrying gluons with no quarks inside. The results were announced on August 5 at the International Conference on High Energy Physics in Natal, Brazil.global.chinadaily

The discovery confirms a long-standing prediction of quantum chromodynamics, the theory describing the strong nuclear force that holds atomic nuclei together.

A Decade of Data

The BESIII Collaboration, operating the Beijing Electron Positron Collider II (BEPCII) under the Chinese Academy of Sciences' Institute of High Energy Physics, found that a particle called X(2370) — first detected in 2011 — is predominantly a glueball. Researchers analyzed more than 10 billion J/ψ meson decay events to build their case. Out of those billions of collisions, only about 5,000 yielded the target signal.sciencealert+1

In 2024, the team published measurements of X(2370)'s mass and spin parity in Physical Review Letters, finding exact agreement with theoretical predictions for the lightest glueball. In their latest analysis, they confirmed the particle's "flavour-singlet" nature — meaning it decays without preference for any specific type of quark — which researchers call "the most important characteristic of a glueball."wionews+1

'Unprecedented Form of Matter'

"We found it 15 years ago, but confirming its identity was extremely difficult. We went through a great deal of effort and built a complete chain of evidence before announcing it to the international community," said Jin Shan, a professor at Nanjing University who led the finding.global.chinadaily

Jin described the glueball as an "unprecedented form of matter" that "not only enables the theory describing strong interactions to pass its most rigorous test, but also vastly expands the boundaries of our understanding of the physical world."sciencealert+1

International Praise

The discovery has drawn recognition from physicists abroad. Colin Morningstar, a professor at Carnegie Mellon University, called the result "a monumental achievement for fundamental physics," while William Detmold, a theoretical physicist at MIT, said the discovery "ticks all the right boxes."global.chinadaily

Wang Yifang, an academician at the Chinese Academy of Sciences, placed the achievement in historical perspective: "This discovery was the result of five generations of scientists working over four decades. Many people left along the way because the task seemed too difficult. Those who stayed finally got the answer."global.chinadaily