Collisions of oxygen and neon nuclei have helped scientists gain deeper insights into the properties of quark-gluon plasma and confirmed the asymmetric shape of the neon nucleus.

Quark-Gluon Plasma: A Window into the Early Universe

Studying atomic nucleus collisions allows physicists to investigate quark-gluon plasma (QGP)—a unique state of matter that existed in the first microseconds after the Big Bang, before atoms formed. During this period, space was filled with a dense, hot plasma of free particles.

Until recently, experiments on QGP at the Large Hadron Collider (LHC) were conducted using heavy ions such as xenon or lead, which made it possible to create the largest possible droplets of plasma. This summer, for the first time in history, the LHC hosted collisions of light nuclei—oxygen and neon. To achieve this, scientists had to modify the standard accelerator configuration, which is usually filled with proton beams.

First Experimental Results

Over six days, the ALICE, ATLAS, CMS, and LHCb experiments collected new data, which was presented at the Initial Stages conference. Researchers focused on measuring subtle patterns in the angles and directions of particles emitted as the QGP droplet expands and cools. These parameters reflect distortions in the collision zone of the nuclei.

Hydrodynamics and Nuclear Shape

The particle behavior patterns resembled liquid flows, so scientists applied hydrodynamic models similar to those used for ordinary fluids. This approach enabled a more precise study of QGP properties and the geometry of the colliding nuclei. Modeling showed that oxygen and neon collisions provide more accurate data on these flows than collisions involving protons or heavy ions.

The ALICE, ATLAS, and CMS collaborations observed significant elliptic and triangular flow in oxygen and neon collisions. It was found that the nature of the flow depends on the type of collision—whether it is glancing or head-on. The agreement between theoretical predictions and experimental data was comparable to results for heavy ions, despite the smaller system size.

The Geometry of the Neon Nucleus and New Discoveries

Scientists believe that the flow parameters in light nucleus collisions are determined by their geometry. The results confirmed the elongated, bowling-pin-like shape of the neon nucleus and demonstrated that hydrodynamic flows arise in various collision systems at the LHC.

Collisions of light ions have opened a new chapter in QGP research. Neon and oxygen nuclei are not only smaller than lead or xenon, but also have a less regular shape. This allows researchers to obtain important data on the minimal nucleus size required for QGP formation.

Additional Confirmations and the Significance of the Results

Special attention was given to studying the shape of the neon nucleus. Theoretically, it should be elongated, like a bowling pin. New experiments at the LHC have refined this picture. The LHCb collaboration presented additional results confirming the neon nucleus shape, obtained from collisions of lead with argon and neon, using data recorded in 2024 at the SMOG facility.

“Taken together, these results offer a fresh perspective on nuclear structure and on how matter emerged after the Big Bang,” noted CERN’s Director for Research and Computing, Joachim Mnich.