Researchers investigate new experimental techniques to measure the extremely intense magnetic fields generated in heavy-ion collisions

Heavy-ion collisions involve the collision of positively charged nuclei of heavy elements at nearly the speed of light. These collisions create a special state of matter called the quark-gluon plasma (QGP), accompanied by intense magnetic fields, resembling the early universe. However, the evolution of these magnetic fields over time has been hard to track. In this study, researchers review the recent experimental efforts to study the time-dependent evolution of magnetic fields generated in these collisions.

In heavy-ion collisions, charged nuclei of heavy elements like copper (Cu), gold (Au), and lead (Pb) are smashed together at nearly the speed of light. The main goal of these collisions is to create and study a special state of matter called the quark-gluon plasma (QGP). Quarks and gluons, which make up subatomic particles like neutrons and protons, collectively known as hadrons, are usually confined inside these particles. But in the QGP, quarks and gluons become free, resembling the conditions of the early universe, just after the Big Bang. Such experiments are conducted mainly at two facilities, the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory and the Large Hadron Collider (LHC) at the European Organization for Nuclear Research. Measurements from these experiments can offer crucial insights into fundamental physics.

An important aspect of heavy-ion collisions is the generation of intense magnetic fields, reaching 10¹⁸ Gauss, millions of times stronger than those found in neutron stars. Although the well-known classical Maxwell’s equations for electrodynamics can reliably estimate the maximum strength of the magnetic field of these collisions, understanding its evolution over time is quite difficult. This is because the magnetic field lasts for only an extremely tiny fraction of a second and depends on how the QGP behaves at different temperatures. Fortunately, new experimental observations can help researchers study how these magnetic fields evolve.

In a new study published in the journal Research on June 24, 2025, a research team explored the latest experimental efforts to detect the intense magnetic fields produced in heavy-ion collisions. “In heavy ion-collisions, only the positively charged nuclei that collide head-on generate a deconfined QGP,” explains Dr. Diyu Shen from the Key Laboratory of Nuclear Physics and Ion-Beam Application (MOE) at Fudan University in China. “In most collisions, however, the nuclei do not fully overlap. The positively charged spectator protons that remain outside the main overlapping region, while moving alongside the heavy-ion beams, generate intense magnetic fields in their vicinity. The strength of this magnetic field varies over multiple collision-events and depends on the spatial position of the protons.” By using observables sensitive to different stages of the magnetic field, researchers can experimentally study the magnetic field’s evolution over time.

In the study, the team reviewed several experimental techniques that use this innovative approach. One method involves utilizing ultraperipheral collisions (UPCs), where two heavy ion nuclei pass each other with a distance greater than the sum of their radii. These UPCs are sensitive to the spatial distribution of protons inside the nuclei and can be used to estimate the strength of the generated magnetic fields.

Another key method is to study the charge-dependent motion of the particles after collisions. When charged particles move through a magnetic field experience Lorentz and Coulomb forces, which change their trajectories. This further creates an electric field in the QGP, following Faraday’s law of induction. Together, these effects cause positive and negative particles to behave differently. This charge-dependent motion acts as a fingerprint of the magnetic field created during the collision In fact, recent measurements from collisions of gold (Au), ruthenium (Ru), and zirconium (Zr) nuclei, as well as low-energy gold collisions studied by the STAR detector at RHIC, have successfully detected signals of this charge-dependent flow of particles, that aligns with the above electromagentic effects.


The study also highlighted how magnetic fields in heavy-ion collisions can change the polarization of special particles called hyperons and anti-hyperons. This spin polarization effect has been observed in high-energy gold (Au) collisions at RHIC and lead (Pb) collisions at the LHC. By measuring the small differences in spin polarization between hyperons and antihyperons, researchers can estimate the strength and lifetimes of magnetic fields generated during collisions.

“Our analysis shows that experimental measurements of magnetic field at various stages of heavy-ion collisions are essential for mapping out their evolution,” notes Dr. Shen.
“For instance, the directed flow of D⁰ mesons is believed to be sensitive to the early-stage magnetic field.”

This study serves as a comprehensive resource for further research into heavy-ion collisions and QGP, paving the way for unlocking the mysteries of the universe.

The complete study is accessible via DOI: 10.34133/research.0726.

About Research by Science Partner Journal
Launched in 2018, Research is the first journal in the Science Partner Journal (SPJ) program. Research is published by the American Association for the Advancement of Science (AAAS) in association with Science and Technology Review Publishing House. Research publishes fundamental research in the life and physical sciences as well as important findings or issues in engineering and applied science. The journal publishes original research articles, reviews, perspectives, and editorials. IF = 10.7, Citescore = 13.3.