X(2370) emerges as glueball-dominated particle in collider experiments

At the International Conference on High Energy Physics held in Brazil, physicists announced a groundbreaking finding: the X(2370) particle has been identified as predominantly composed of a pseudoscalar glueball. This determination was made by the BESIII Collaboration, following over 15 years of dedicated research. The key evidence came from analyzing the decay patterns of J/ψ particles produced at the Beijing Electron Positron Collider. The results show that the X(2370) has spin-parity quantum numbers of 0⁻⁺, matching precisely with theoretical predictions for a pseudoscalar glueball. The journey to this discovery began in 2011 when the BESIII team first detected the X(2370) particle through the decay of J/ψ mesons. For more than a decade, researchers worked intensively to refine their understanding of this particle’s properties. In 2024, using a significantly larger dataset, comprising 10 billion J/ψ particles, the collaboration was able to measure the spin-parity quantum numbers for the first time. These measurements confirmed that the X(2370) aligns with the characteristics predicted for a pseudoscalar glueball, offering compelling support for its identity. Gluons, the fundamental particles responsible for mediating the strong nuclear force, are known to interact with each other under certain conditions. This self-interaction leads to the formation of bound states known as glueballs, which are purely composed of gluons rather than quarks. Unlike ordinary hadrons, which consist of quark-antiquark pairs or triplets, glueballs represent a novel form of matter. Their existence is a critical prediction of quantum chromodynamics (QCD), the theory that governs the behavior of quarks and gluons. For nearly five decades, scientists have pursued the detection of glueballs, yet definitive proof remained elusive. The Beijing Electron Positron Collider has played a central role in these efforts, as it enables the production of large quantities of J/ψ mesons. These mesons serve as ideal candidates for studying glueballs because their decay processes can reveal signatures of such exotic particles. The BESIII Collaboration has consistently prioritized this area of research, leading to a series of breakthroughs that culminated in the current findings. In addition to confirming the spin-parity quantum numbers, recent studies by the BESIII team uncovered new decay channels of the X(2370) particle. Most notably, they established its "flavor-singlet" nature, a defining feature of a genuine glueball. This property indicates that the X(2370) does not contain any specific flavor of quark, further supporting its classification as a pure glueball. Collectively, these discoveries form a robust body of experimental evidence, reinforcing the hypothesis that the X(2370) is primarily a pseudoscalar glueball. The implications of this discovery extend beyond particle physics. It represents a direct validation of QCD’s non-Abelian gauge structure, particularly at low energy scales. Asymptotic freedom, a foundational principle of QCD, has already been confirmed through high-energy experiments, but the confirmation of glueballs offers additional insight into how QCD behaves under different conditions. Moreover, the identification of a glueball opens new avenues for exploring the fundamental nature of matter and the forces that bind it.