After 50 Years, Physicists May Have Finally Found a Particle Made of Pure Force

Gluons are the quantum ‘Gorilla Glue’ involved in binding quarks together, ScienceAlert reminds us. But for nearly 50 years, physicists have hunted for “glueballs”, exotic particles predicted by this theory of the strong interaction — the only type of particle in nature composed entirely of force mediators:

Now, a collaboration working at a collider in Beijing says it has the clearest evidence yet that a known particle called X(2370) is dominated by one of these elusive states… Physicists sifted through the wreckage of high-energy particle collisions to find strong evidence of this glueball, made predominantly of gluons — massless force carriers of the strong interaction between quarks… The new evidence for this exotic, unstable glueball’s ephemeral existence comes from a recent preprint on arXiv, presented at the International Conference on High Energy Physics in Brazil… This collaboration uses the Beijing Electron Positron Collider II, a particle accelerator and collider that smashes electrons into their antimatter counterparts, called positrons, to probe perplexing particle physics.

The resultant glueball is an “unprecedented form of matter,” says Jin Shan, a particle physicist at Nanjing University and one of the research team’s leaders. “It 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,” he told Fan Chen at South China Morning Post… Previously, in a study published in the journal Physical Review Letters in 2024, the researchers analyzed 10 billion meson decay events. They measured the X(2370) particle’s mass and spin parity — a property that dictates its interactions and almost-instantaneous decay — for the first time, finding complete agreement between their experimental values and predictions. Now, they’ve identified its additional decay modes and determined its flavor-singlet nature, “the most important characteristic of a glueball….”

The authors describe their work as the clearest experimental result to emerge from nearly 50 years of glueball searches, supporting the long-standing theoretical prediction that gluons can bind together into a new form of matter.

The discovery “”highlights advances in technology and analytical techniques that have recently revealed another decades-in-the-making physics mystery,” the article points out.

“More experiments are needed to further confirm and constrain the prototypes of the highly esoteric glueball; in other words, more particle smashing.”

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