CERN ALICE experiment observes unexpected drop in J/ψ production at sub‑proton scales

Physicists at CERN have used the ALICE experiment at the Large Hadron Collider to achieve an unprecedented view inside atomic nuclei, allowing them to test competing theories of gluon behavior. By measuring particle production with a spatial resolution that reaches structures as small as roughly one‑quarter the diameter of a proton, the team has opened a new window on the sub‑nuclear landscape that was previously inaccessible.

The high‑resolution data reveal a marked decrease in the production of J/ψ mesons at the smallest distance scales, a pattern that standard models based on nuclear shadowing cannot readily account for. This discrepancy suggests that alternative mechanisms may dominate gluon dynamics in tightly packed nuclear environments, providing a critical benchmark for refining theoretical descriptions of strong‑force interactions. The findings mark a significant step toward resolving long‑standing uncertainties in quantum chromodynamics and could guide future experimental and theoretical work in high‑energy nuclear physics.