Glueball detection supports key prediction of quantum physics

After almost two decades of searching, the BESIII Collaboration has presented evidence suggesting the particle X (2370), first discovered in 2011, is “mostly made up of glueballs.” Researchers at the international experiment, presenting at the International Conference on High Energy Physics in Natal, Brazil, analyzed nearly ten billion J/ψ decays to determine the particle’s quantum properties. This finding offers the strongest evidence yet for these force-based particles and supports a key prediction of quantum chromodynamics. Bruce Yabsley of the University of Sydney notes that the cumulative evidence is substantial.

BESIII Collaboration Identifies X(2370) as Potential Glueball Candidate

This conclusion stems from an analysis of nearly ten billion J/ψ decays, a process where a heavier particle breaks down, potentially revealing the fleeting existence of glueballs. Researchers meticulously examined these decays, seeking a particle with characteristics aligning with theoretical predictions for the lightest glueball, a composite of gluons, the force-carrying particles binding quarks within atomic nuclei. For thirteen years, scientists at BESIII scrutinized data, ultimately determining the spin parity of X (2370) in 2024.

The resulting measurement revealed the particle to be a ‘pseudoscalar’ with a spin parity of 0−+, a property consistent with the predicted behavior of the lightest glueball. However, establishing a definitive identification required overcoming the challenge that numerous particles can exhibit similar properties. The team’s persistence, coupled with the unique capabilities of the BESIII experiment at the Institute of High Energy Physics (IHEP) in China, proved crucial in building a persuasive case.

BESIII’s design, specifically tailored to study electron-positron collisions, generates a substantial number of J/ψ particles, providing ample opportunities to observe their decay products. Yanhping Huang, a particle physicist at IHEP, recalls the initial excitement surrounding the identification of X (2370) during her doctoral studies. “At that time it was quite exciting for us,” Huang says, noting the particle’s mass was already suggestive of a glueball composition.

Bruce Yabsley, a particle physicist at the University of Sydney in Australia, who reviewed the BESIII results, acknowledges the strength of the accumulated evidence. The potential confirmation of glueballs extends beyond validating quantum chromodynamics; it also offers insights into the origin of mass itself. Protons, though composed of quarks, possess a mass exceeding the sum of their constituent quark masses.

This discrepancy suggests that the strong interactions between gluons contribute significantly to the overall mass, a phenomenon that direct observation of glueballs could help elucidate. Shan Jin, a particle physicist at Nanjing University in China, who presented the results at the conference, emphasizes the importance of BESIII’s ability to produce vast numbers of J/ψ particles, enabling detailed studies of their decay pathways and ultimately, a deeper understanding of the fundamental forces governing the universe.

Quantum Chromodynamics Confirmed by Observed Glueball Spin Parity

The Beijing Spectrometer III (BESIII) Collaboration has refined understanding of the X (2370) particle, now identifying it as predominantly composed of glueballs, clusters of gluons, and providing compelling support for predictions within quantum chromodynamics. Confirming the glueball composition of X (2370) is significant because it offers direct evidence that gluons, the force-carrying particles binding quarks, can interact with each other. This self-interaction is a fundamental prediction of quantum chromodynamics, the theory governing the strong force within atomic nuclei.

Ulrik Egede, an experimental particle physicist at Monash University in Melbourne, Australia, who reviewed the presentation of the results, states, “It is quite convincing evidence.” BESIII’s unique capabilities were essential to this discovery. The experiment, located at the Beijing Electron-Positron Collider II, is specifically designed to study collisions between electrons and positrons, creating short-lived particles that can decay into glueballs.

The abundance of J/ψ particles produced by BESIII allowed researchers to meticulously study their decay patterns, ultimately leading to the determination of X (2370)’s spin parity. The observation of glueballs not only validates quantum chromodynamics but also deepens understanding of how mass originates within matter, offering insights into the fundamental building blocks of the universe.