Using Nuclear Shapes to Study How Particles Flow in Collisions Between Light Ions

The Science   

Newswise — Physicists are searching for signs that even the smallest high-energy nuclear collisions can create a hot, dense state of matter known as the quark-gluon plasma (QGP). These small collisions are of light nuclei that have relatively low numbers of protons and neutrons. Researchers studied the collisions of two different light nuclei: oxygen-16 and neon-20. Oxygen-16 has a relatively round shape. In contrast, neon-20 has an unusual “bowling-pin” nuclear shape. Using nuclear structure calculations and hydrodynamic simulations, the team showed that the unusual neon-20 shape leaves a distinct fingerprint in how particles flow after collisions. By comparing oxygen-16 and neon-20 collisions, the scientists could cancel out many uncertainties. This work makes it possible to study collective behavior within the QGP with higher precision.

The Impact

The QGP existed at the beginning of the universe just after the Big Bang. Studying it helps scientists better understand the building blocks of our universe. Previously, physicists thought that only high-energy collisions of heavy ions could create the QGP. Researchers at the Relativistic Heavy Ion Collider (a DOE Office of Science User Facility) and the Large Hadron Collider (LHC) have been studying how colliding lighter ions can produce the QGP.  This specific work provided important theoretical motivation for the neon-20-neon-20 collisions run at the LHC in July 2025. The “bowling-pin” nuclear shape geometry of neon-20 amplifies the elliptic flow. Oxygen-16 provided a baseline. By comparing the two, scientists disentangled the effects of nuclear geometry from other sources of uncertainty. This opens a new path for studies of QGP and strengthens the bridge between nuclear structure theory and high-energy nuclear physics. The new LHC results on neon-20-neon-20 and oxygen-16-oxygen-16 collisions appear to confirm several key predictions made in this work.

Summary

An international team of researchers combined ab initio nuclear structure calculations with event-by-event hydrodynamic simulations of neon-20-neon-20 and oxygen-16-oxygen-16 collisions at LHC energies. The researchers used two methods to perform the nuclear structure calculations: the projected generator coordinate method and nuclear lattice effective field theory.  The results showed that the non-uniform flow of particles following neon-20-neon-20 collisions is enhanced compared to oxygen-16-oxygen-16. They also showed that correlations between flow and particle momentum carry an imprint of neon’s elongated shape. These predictions are robust against systematic uncertainties and appear to be confirmed by data from the LHC runs performed in July 2025.

Funding

Funding for the researchers comes from Deutsche Forschungsgemeinschaft, the U.S. Department of Energy’s Nuclear Physics program, and the U.S. National Science Foundation. This work is also supported in part by the European Research Council and the Spanish MCIU. The research used computational resources from GENCI-TGCC, CCRT, the Gauss Centre for Supercomputing e.V., the Oak Ridge Leadership Computing Facility (a DOE Office of Science User Facility), and the TUBITAK ULAKBIM High Performance and Grid Computing Center.