CERN Physicists Witness the Transformation of Lead into Gold

Collisions involving high-energy lead nuclei at CERN’s Large Hadron Collider generate a powerful electromagnetic field capable of displacing protons and converting lead into ephemeral gold nuclei.

The transformation of base metal lead into the precious metal gold was a long-held aspiration of medieval alchemists.

This enduring pursuit, known as Chrysopia, may have been spurred by the recognition that the relatively common lead, with its dull gray color, bears resemblance to gold.

It has since been established that lead and gold are fundamentally different chemical elements, and that chemical means cannot facilitate their conversion.

The advent of nuclear physics in the 20th century uncovered the possibility of transforming heavy elements into others through processes such as radioactive decay or in laboratory settings involving bombardment by neutrons or protons.

Gold has been artificially generated through such means previously, but physicists from the Alice Collaboration at CERN’s Large Hadron Collider (LHC) have recently measured lead’s conversion into gold using a novel mechanism that relies on close interactions between lead nuclei at the LHC.

High-energy collisions between lead nuclei can lead to the formation of quark-gluon plasma, a state of high temperature and density believed to represent conditions shortly after the Big Bang, initiating phenomena we now recognize.

Simultaneously, in more frequent instances where nuclei narrowly miss each other without direct contact, the strong electromagnetic fields they generate can provoke photon-nucleus interactions, potentially uncovering more exploration avenues.

The electromagnetic field produced by the nucleus is particularly potent due to its 82 protons, each carrying a fundamental charge.

Additionally, when lead nuclei are accelerated to extreme speeds at the LHC, the electromagnetic field lines become compressed into thin layers, extending laterally in the motion direction, generating transient pulses of photons.

This phenomenon often triggers electromagnetic dissociation, where photons interact with the nucleus, causing vibrations in its internal structure and leading to the release of a limited number of neutrons and protons.

To fabricate gold (with 79 protons), three protons must be removed from the lead nuclei in the LHC beam.

“It is remarkable to witness our detectors managing direct collisions that produce thousands of particles, while being sensitive to scenarios where merely a few particles are generated,” said a researcher.

The Alice team employed a zero degree calorimeter (ZDC) to quantify the number of photon-nucleus interactions, correlating them to the emission of zero, one, two, and three protons related to the production of lead, thallium, mercury, and gold, respectively.

While the creation of thallium and mercury occurs more frequently, results indicate that the LHC currently generates gold at a rate of approximately 89,000 nuclei from lead collisions at the Alice collision point.

These gold nuclei emerge from collisions at extremely high energies, colliding with LHC beam pipes or collimators at various downstream points and swiftly fragmenting into individual protons, neutrons, and other particles, lasting mere seconds.

The analysis from Alice shows that roughly 86 billion gold nuclei were produced during four significant experiments across two runs of the LHC, equating to only 29 picograms (2.9*10^-11 g) in mass.

With ongoing upgrades to the LHC enhancing its brightness, Run 3 yielded almost double the amount of gold as observed in Run 2, although the overall quantity remains trillions of times less than what is necessary for jewelry production.

Though the technological aspirations of medieval alchemists have been partially fulfilled, their dreams of acquiring wealth have yet again been dashed.

“Thanks to the distinctive capabilities of Alice’s ZDC, our current analysis marks the inaugural systematic detection and examination of gold production signatures at the LHC,” states Dr. Uliana Dmitrieva, a member of the Alice Collaboration.

“These results extend beyond fundamental physics interests and serve to test and refine theoretical models of electromagnetic dissociation, improving our understanding of beam loss— a significant factor influencing the performance limitations of the LHC and future colliders,” adds Dr. John Jowett, also of the Alice Collaboration.

A new study will be published in the journal Physical Review C.

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S. Acharya et al. (Alice Collaboration). √s_NN= 5.02 Proton emission in ultra-fine Pb-Pb collisions at TeV. Phys. Rev. C 111, 054906; doi:10.1103/PhysRevC.111.054906