Physicists have recreated a fleeting state of matter believed to have filled the Universe moments after the Big Bang—by colliding atomic nuclei far smaller than the heavy lead ions traditionally used in such experiments. The result, achieved by the international ALICE collaboration at CERN, provides new evidence that quark-gluon plasma can emerge in collisions involving oxygen and neon nuclei. These miniature fireballs, lasting for an unimaginably brief fraction of a second, could help scientists investigate both the earliest history of the cosmos and the hidden structure of atomic nuclei.
The experiment took place at the Large Hadron Collider, where beams of atomic nuclei can be accelerated to nearly the speed of light before being directed into head-on collisions. At energies of 5.36 teraelectronvolts per nucleon pair, oxygen-16 and neon-20 nuclei were smashed together under conditions of extraordinary temperature and energy density. For an instant, the protons and neutrons inside the nuclei were no longer the dominant structures. Instead, their fundamental constituents—quarks and gluons—were able to move within a tiny, rapidly expanding region of deconfined matter.
This state, known as quark-gluon plasma, is thought to have existed during the first millionth of a second after the Big Bang. The early Universe was then far hotter than any environment found naturally today, and ordinary atomic nuclei had not yet formed. Quarks and gluons moved through a dense, fluid-like medium before the Universe expanded and cooled enough for them to become bound into protons and neutrons. Eventually, those particles formed atomic nuclei, atoms, stars, planets and the material from which life emerged.
For decades, researchers generally associated the creation of quark-gluon plasma with collisions between the heaviest available nuclei, particularly lead. Heavy-ion collisions produce large amounts of energy and many interacting particles, making them favorable environments for generating the plasma. The new ALICE result challenges the assumption that such extreme conditions require the largest nuclei. By observing collective patterns in the particles produced after oxygen-oxygen and neon-neon collisions, the researchers found signs that the smaller systems can also behave like rapidly expanding droplets of strongly interacting matter.
The plasma itself cannot be photographed or detected directly because it disappears almost immediately after the collision. Instead, scientists reconstruct its properties from the thousands of particles created as it cools. One of the most informative signals is anisotropic flow, the uneven distribution of particles emerging at different angles around the collision axis. This flow reflects how the original collision zone was shaped and how the hot medium expanded. If the matter behaves collectively, its final particle pattern preserves a memory of the geometry and pressure gradients present at the instant of impact.
The neon results were especially revealing because the neon-20 nucleus is not perfectly spherical. Its internal structure is expected to be elongated, resembling a microscopic bowling pin rather than a ball. When two such nuclei collide, their orientation and shape can influence the geometry of the region where the plasma forms. Oxygen-16, by comparison, produces a more rounded collision profile. The differing flow patterns measured by ALICE therefore act like shadows cast by invisible objects: although the nuclei cannot be observed in their high-energy collision state, their shapes can be inferred from the motion of the particles they generate.
“The particles from the primordial matter are directly governed by the geometric shape of the atomic nucleus,” explains Emil Gorm Dahlbæk Nielsen of the Niels Bohr Institute, a co-author of the study. In a spherical collision, the pressure gradients tend to generate one characteristic pattern, while an elongated collision creates another. As the plasma expands, those gradients convert the initial spatial asymmetry into momentum anisotropy. By measuring this angular distribution, physicists can connect the final-state particles to the nuclear geometry that existed before the collision.
The finding also reaches into one of nuclear physics’ oldest questions: how protons and neutrons are arranged inside atomic nuclei. Nuclear shape is not merely a visual description. It reflects the balance between the strong nuclear force, collective motion and the quantum structure of the nucleons. The strong force binds quarks inside protons and neutrons and also governs how those composite particles interact within a nucleus. Traditional experiments often probe nuclear shapes at relatively low energies through rotational spectra, electromagnetic transitions and other carefully controlled measurements. The ALICE approach offers a radically different method, using the expansion of ultra-hot matter as a high-energy probe of nuclear structure.
You Zhou, who led the work and was until recently affiliated with the Niels Bohr Institute at the University of Copenhagen, says the experiment pushes the lower boundary for the size of a nuclear system capable of producing primordial matter. The precise threshold remains unknown, however. A central challenge for future research will be determining whether the same collective behavior survives in still smaller collisions. The collaboration plans to investigate lighter systems, potentially including helium-4, to discover where the transition between plasma-like collective behavior and ordinary particle production occurs.
That question matters because small collision systems can behave in surprisingly complex ways. In a large lead-lead collision, the presence of a dense, extended medium makes collective effects comparatively easier to identify. In oxygen or neon collisions, the system is much smaller and exists for an even shorter time, so alternative processes must be examined carefully. The new measurements nevertheless show that nuclear geometry can leave a measurable imprint even at this scale. If confirmed and developed through additional experiments and theoretical calculations, the method could become a new tool for studying exotic nuclei that are difficult to investigate with conventional techniques.
The results, published in Physical Review Letters as an Editors’ Suggestion, demonstrate how research into the birth of the Universe can intersect with the detailed study of matter at the nuclear scale. The same collision can function as a cosmic time machine and a microscope: it recreates conditions associated with the earliest moments of existence while revealing information about the shape and organization of atomic nuclei. Each microscopic “Little Big Bang” lasts less than the blink of an eye, but the particles it produces carry traces of the event long enough for detectors to record them. By decoding those traces, physicists are narrowing the gap between the first moments of the cosmos and the forces that still shape matter today.
Subject of Research: Quark-gluon plasma, nuclear geometry, anisotropic flow, and oxygen-oxygen and neon-neon collisions at the CERN Large Hadron Collider.
Article Title: Evidence of Nuclear Geometry-Driven Anisotropic Flow in O+O and Ne+Ne Collisions at √sNN = 5.36 TeV
News Publication Date: 17-Aug-2026
Web References: https://journals.aps.org/prl/abstract/10.1103/gymp-vp87
References: Physical Review Letters, DOI: 10.1103/gymp-vp87
Image Credits: ALICE@CERN
Keywords
Quark-gluon plasma, Big Bang, CERN, Large Hadron Collider, ALICE collaboration, oxygen-16, neon-20, nuclear physics, anisotropic flow, atomic nuclei, strong force, primordial matter, particle collisions, Niels Bohr Institute
Tags: atomic nuclei collision experimentsBig Bang recreated in laboratoryCERN Large Hadron Collider researchearly universe originsfundamental particle constituentshigh-energy particle physicshigh-temperature particle collision studiesnuclear physics and structureproton and neutron collision experimentsquark-gluon plasma evidencequark-gluon plasma formationsmall-scale fireball experiments
