Oxygen and Neon Collisions Reveal a Tiny Quark–Gluon Plasma

CERN’s 2025 light-ion run produced strong evidence that smashing oxygen-16 and neon-20 nuclei together at the Large Hadron Collider can generate a tiny, rapidly expanding medium with collective behavior associated with quark–gluon plasma (QGP). The result matters because QGP studies have traditionally focused on much heavier collision systems, especially lead–lead collisions.

The evidence comes primarily from the way particles emerge from the collisions. Rather than flying out randomly, the debris shows coordinated, anisotropic flow whose patterns depend on the geometry of the incoming nuclei. That makes the experiment both a test of QGP-like collectivity and a new way to study nuclear shape.

What ALICE observed in the 2025 run

Between 29 June and 9 July 2025, the LHC carried out dedicated collisions involving oxygen–oxygen and neon–neon pairs, as well as oxygen–proton collisions. The oxygen–oxygen and neon–neon data were collected at a centre-of-mass energy of 5.36 TeV per nucleon pair.

ALICE measured elliptic flow and triangular flow—two forms of anisotropic particle emission—in both light-ion systems. The flow coefficients were sizable and varied with collision centrality, or how directly the two nuclei struck each other. Hydrodynamic models that incorporate the collision geometry describe the observed patterns, providing evidence for collective dynamics in these unusually small systems.

Why neon’s shape made the result especially useful

Oxygen-16 is comparatively round, giving researchers a useful baseline. Neon-20, by contrast, has a predicted elongated or prolate structure often compared with a bowling pin. When two neon nuclei collide, that deformation can leave a stronger imprint on the angular distribution of the particles produced afterward.

The comparison between the two collision systems is therefore more informative than studying either one alone. A stronger elliptic-flow signal in central neon–neon collisions, relative to oxygen–oxygen collisions, is consistent with the idea that the initial nuclear shape helps determine the final particle flow.

In effect, the debris acts as an indirect image of the nuclei at the instant of impact. This is one reason the result has implications beyond QGP physics: high-energy collisions can now complement traditional nuclear-structure measurements and calculations of how protons and neutrons are distributed inside a nucleus.

Did all four LHC experiments independently confirm QGP?

The main LHC collaborations—ALICE, ATLAS, CMS and LHCb—reported signs of collective behavior in the light-ion data. CERN described these as new indications that oxygen and neon collisions may produce the extreme state of matter associated with the Universe’s first microseconds.

That convergence is significant, but “indication” is the careful word. Collective flow is a central signature of QGP-like behavior, yet the light-ion systems are small enough that other effects can complicate the interpretation. The results support the onset of QGP-like collectivity; they should not be presented as an isolated, conclusive proof that every collision creates a fully developed plasma.

Why the finding changes the research question

The 2025 results push the field toward a more precise question: how small can a collision system be while still producing QGP-like collective behavior? Until now, the clearest signals came from collisions involving substantially heavier nuclei. Oxygen and neon provide a new intermediate scale for testing where the transition from ordinary particle production to collective, deconfined matter occurs.

They also create a controlled way to separate two issues that are often difficult to disentangle: the properties of the hot medium and the shape of the nuclei that created it. Comparing a relatively round nucleus with a deformed one gives theorists a sharper test of hydrodynamic calculations and nuclear-structure models.

The broader payoff is a closer connection between two areas of physics. Nuclear-structure experiments and calculations describe the internal geometry of ordinary nuclei at low energies, while the LHC probes matter at extreme temperature and energy density. Light-ion collisions connect those scales, using the final-state flow to test both the initial nuclear configuration and the behavior of the resulting medium.

What researchers will look for next

Further measurements will determine whether the observed collective patterns persist as the collision system becomes still smaller and will help establish the minimum conditions required for QGP-like behavior. That threshold could refine models of deconfined quarks and gluons and improve our understanding of the extreme matter present during the Universe’s earliest moments.

For now, the central conclusion is measured but important: oxygen and neon are light compared with the nuclei normally used in heavy-ion physics, yet their collisions produce flow patterns that carry both the signature of nuclear geometry and strong evidence of collective QGP-like dynamics.