What is a glueball? Chinese-led team finds rare particle made entirely of force

In a monumental discovery, a Chinese-led international scientific team has verified the existence of a unique form of matter known as the glueball. This extraordinary discovery was unveiled at the International Conference on High Energy Physics, which convenes every two years to showcase the most significant advancements in the field.

The research team, comprising around 700 scientists from 15 countries, culminated their 15-year endeavor by presenting compelling evidence of glueballs, using the Beijing Electron Positron Collider II. Glueballs are composed of gluons, particles that act as carriers of the force binding quarks together into larger particles such as protons and neutrons, which in turn form atoms, the building blocks of all matter in the universe.

The concept of glueballs has been postulated for 50 years, as scientists hypothesized that gluons, unlike photons, attract each other while carrying the strong force. However, concrete evidence remained elusive until the team’s groundbreaking findings were presented at the conference. Utilizing the collider to accelerate electrons and their antiparticles at near-light speed, the team produced J/psi particles, which, upon decay, presented an ideal environment for identifying the presence of glueballs.

In 2011, the team identified a new particle that was probable to be a glueball, and subsequently, after meticulous analysis of approximately 10 billion J/psi particles, they measured its mass and various properties in 2024. This revelation led to a critical breakthrough: a glueball carries no "flavor" information, distinguishing it from conventional particles like protons and neutrons, which comprise quarks of varying flavors.

Co-leader of the team, Prof. Huang Yanping from the Institute of High Energy Physics of the Chinese Academy of Sciences, explained to Guangming Daily that the discovery marked a profound shift, indicating that "force itself has become a physical entity," akin to messengers delivering letters transforming into a sculptural formation.

Prof. Jin Shan, another leader from Nanjing University, emphasized that the findings validated an "unprecedented form of matter," enhancing the understanding of the strong interactions and pushing the boundaries of our comprehension of the physical world. The high-performance collider, inaugurated in 1988, underwent a major upgrade in May, tripling its peak luminosity – a crucial parameter that amplifies the likelihood of generating rare particle events, significantly expediting the discovery process.