Physicists are rethinking proton and neutron structure, arguing baryon number may be carried by gluon-field junctions rather than just three valence quarks, based on heavy-ion collision studies.

This junction picture suggests baryon number is not simply tied to quarks, implying protons and neutrons are more complex than a trio of valence quarks.

Experiments with zirconium-96 and ruthenium-96 show baryon number rearrangement does not track electric charge movement as closely as the valence-quark model would predict, indicating different carriers for baryon number and charge.

In high-energy perturbative QCD, quarks can appear isolated and both models align, but in the lattice QCD regime inside protons or quark-gluon plasma, their predictions diverge.

The STAR collaboration at RHIC compared the baryon junction model and the valence quark model against data to see which better matches reality.

Head-on gold nucleus collisions and near-miss events show energy dependence of net baryon scattering aligns more with the junction model, which underpredicts in the valence-quark picture.

Researchers plan further studies at other facilities and anticipate insights from the Electron-Ion Collider that could sharpen baryon probes.

The idea that baryon number could be carried by a gluon-field Y-shaped junction predates QCD, with a 1996 model proposing this mechanism.

The work contributing to understanding proton structure and baryon-number distribution in nuclear collisions is published in Science.