Researchers at CERN’s Large Hadron Collider have completed a detailed study of gluon distribution within atomic nuclei, according to findings published in Physical Review Letters. The study, led by University of Kansas physicist Daniel Tapia Takaki as part of the ALICE experiment, represents the first multidimensional measurement of incoherent J/ψ photonuclear production that simultaneously tracks both interaction energy and momentum transfer. These dual measurements enabled scientists to examine gluon behavior with previously unattainable precision.
Gluons are fundamental particles responsible for binding quarks together through the strong force. Though quarks are often described as the basic building blocks of matter, the overwhelming majority of visible matter’s mass actually derives from the energy associated with gluons and the strong nuclear force. Understanding gluon behavior inside nuclei is therefore critical to comprehending how matter acquires its mass and physical structure.
To investigate gluon distribution variations, researchers employed a technique using incoherent J/ψ photonuclear production. During Run 2 of the Large Hadron Collider, fast-moving lead nuclei passed near each other without direct collision. The intense electromagnetic fields surrounding these nuclei functioned as beams of high-energy photons, and when one photon struck a nucleus, it produced a J/ψ particle whose creation revealed details about underlying gluon structure. Unlike conventional measurements that average gluon distribution across entire nuclei, this approach revealed localized changes in gluon density, enabling investigation of structures smaller than individual protons.
The experimental results revealed a striking suppression in J/ψ particle production at the smallest spatial scales examined, with statistical significance of approximately three standard deviations. This unexpected pattern challenges the long-established “nuclear shadowing” model, which had successfully explained previous measurements. The observations instead align with “gluon saturation,” a phenomenon predicted by quantum chromodynamics. In this regime, gluons become so densely packed that they interact strongly with each other, limiting how many can occupy a given region. These findings suggest competing theoretical frameworks for understanding fundamental physics at extremely small scales may require reevaluation.
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