ALICE finds jet quenching in oxygen-oxygen collisions at LHC

August 31, 2026 at 05:53 AM2 min

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The ALICE Collaboration at CERN's Large Hadron Collider reports direct evidence of parton energy loss in oxygen-oxygen collisions at 5.36 TeV per nucleon pair. The result extends jet-quenching evidence to the smallest nuclear system studied so far. Oxygen-16 nuclei, each with eight protons and eight neutrons, provide an intermediate test between proton and lead collisions.

Key Facts

The ALICE Collaboration reports direct evidence of parton energy loss in oxygen-oxygen collisions at 5.36 TeV per nucleon pair.
The Large Hadron Collider completed its first run with oxygen-oxygen and neon-neon collisions in July 2025.
Each fully ionised oxygen-16 nucleus contains eight protons and eight neutrons.
A lead-208 nucleus contains 208 protons and neutrons, making oxygen much lighter than the established heavy-ion workhorse.
Proton-proton and proton-lead collisions have produced flow-like correlations but the direct energy-loss signature remained elusive.

Quark-Gluon Plasma

During the universe's first few microseconds, temperatures were too high for quarks and gluons to remain confined inside protons and neutrons. Matter instead occupied a state called quark-gluon plasma, which behaves less like a thin gas than a strongly coupled liquid with extraordinarily low viscosity. CERN has made microscopic droplets of quark-gluon plasma before by colliding heavy nuclei. The latest advance concerns how small the colliding nuclei can be while still producing a decisive signature.

Oxygen Collisions

In July 2025, the Large Hadron Collider completed its first run with oxygen-oxygen and neon-neon collisions. The LHC brought the oxygen nuclei into collision at a centre-of-mass energy of 5.36 teraelectronvolts per nucleon pair. Oxygen supplies an intermediate test: much smaller than lead, but structured well enough for cleaner comparisons. Smaller proton-based collisions have displayed collective behaviour, but the direct energy-loss signature remained elusive.

Jet Quenching

A violent interaction early in a collision can launch a high-energy quark or gluon, collectively called partons. A parton cannot reach a detector on its own; as the system cools, it fragments into a narrow spray of ordinary particles called a jet. If the parton crosses quark-gluon plasma, it interacts with the medium and surrenders some of its energy, an effect called jet quenching. The ALICE Collaboration analysis of oxygen-oxygen collisions reports direct evidence that energetic quarks and gluons lost energy while crossing the medium.