For centuries, alchemists sought to convert common metals into gold, a phenomenon known as chrysopoeia. Now, thanks to advances in nuclear physics, this ancient aspiration has unexpectedly become a reality at CERN’s Large Hadron Collider (LHC), where scientists have observed a real and measurable process of transmutation from lead into gold, according to a recently published article by the ALICE collaboration in the journal Physical Review Journals.

The transformation observed by ALICE is based on high-energy physical phenomena and mechanisms that can only occur under extreme conditions, such as those recreated in heavy ion collisions at the LHC. In particular, it involves a type of interaction known as an ultra-peripheral collision, in which lead nuclei—each containing 82 protons—approach at speeds close to that of light without directly colliding, generating intense electromagnetic fields capable of inducing unusual subatomic reactions.

When these fields act on the nuclei, they can emit extremely brief photon pulses, which then interact with other particles in the nearby nucleus. This phenomenon, known as electromagnetic dissociation, can destabilize the internal structure of the nucleus and cause the ejection of protons and neutrons. In the specific case of gold creation, the process requires a lead nucleus to lose three protons, reducing its atomic number from 82 to 79, which corresponds to gold (Au).

CERN gold ALICE detector
Illustration of an ultra-peripheral collision where the two lead (208Pb) ion beams at the LHC pass by close to each other without colliding. In the electromagnetic dissociation process, a photon interacting with a nucleus can excite oscillations of its internal structure and result in the ejection of small numbers of neutrons (two) and protons (three), leaving the gold (203Au) nucleus behind. Credit: CERN

This mechanism, which had been theorized but not systematically observed until now, has been measured thanks to the unique capabilities of the ALICE detector, particularly through its Zero Degree Calorimeters (ZDCs). These devices enabled researchers to precisely count the events in which nuclei emitted zero, one, two, or three protons—always accompanied by at least one neutron—indicating the possible formation of new nuclei of lead, thallium, mercury, and, more rarely, gold.

According to the collected data, the ALICE experiment has detected that, although gold production is much less common than that of other neighboring elements, approximately 89,000 gold nuclei are generated per second at the LHC collision point from lead nucleus collisions. However, these gold particles emerge with such high energy that they immediately strike the beam pipe or the accelerator’s collimators, fragmenting almost instantly into protons, neutrons, and other elementary particles. Consequently, the produced gold exists only for a tiny fraction of a second, and cannot be collected or stored.

During the LHC’s second operational cycle, which took place between 2015 and 2018, it is estimated that around 86 billion gold nuclei were formed, amounting to about 29 picograms—30 million times less than the weight of a speck of dust. Although technological advances have allowed this figure to double in the current Run 3 of the collider, the total volume remains negligible from any practical standpoint, especially for those still dreaming of making jewelry from subatomic particles.

It’s impressive to see how our detectors can record head-on collisions that generate thousands of particles, and at the same time be sensitive enough to detect events where only a few particles are involved, said Marco Van Leeuwen, spokesperson for the ALICE collaboration. This instrumental duality has been key in detecting, for the first time systematically, the experimental signature of gold production at the LHC.

For her part, Uliana Dmitrieva, also a member of ALICE, highlighted that thanks to the ZDCs’ unique capability, this pioneering analysis was possible. John Jowett, another team member, emphasized that these results not only expand fundamental knowledge of electromagnetic dissociation, but also help refine theoretical models essential for understanding and predicting beam losses—a critical factor for optimizing the performance of both the LHC and future particle accelerators.

SOURCES

CERN S. Acharya et al., Proton emission in ultraperipheral Pb-Pb collisions at √sNN=5.02 TeV, Physical Review C (2025). DOI: 10.1103/PhysRevC.111.054906

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