Production of various elements in ultraperipheral $^{208}$Pb-$^{208}$Pb collisions at the LHC

TL;DR

This paper models ultraperipheral lead-lead collisions at the LHC, showing that electromagnetic interactions produce specific elements whose cross sections can be inferred from proton emission data, enhancing understanding of nuclear fragmentation.

Contribution

It introduces the RELDIS model to evaluate photonuclear reactions in ultraperipheral collisions, linking element production cross sections to measurable proton emission data.

Findings

Electromagnetic dissociation leads to specific element production.

Cross sections of elements are approximated by proton emission cross sections.

Model predictions align with experimental measurements.

Abstract

As predicted by theory and confirmed by measurements, one, two or three neutrons are emitted frequently in ultraperipheral collisions (UPCs) of heavy relativistic nuclei, in particular, $^{208}$Pb. The exchange of low-energy Weizs\"{a}cker--Williams photons dominates in such interactions. This leads to the excitation and decay of Giant Dipole Resonances (GDR) in colliding nuclei below the proton emission threshold. Less is known about the electromagnetic dissociation of $^{208}$Pb induced by energetic photons leading to violent fragmentation of $^{208}$Pb. The UPCs of lead nuclei at the LHC were modelled with Relativistic ELectromagnetic Dissociation (RELDIS) model to evaluate the contribution of photonuclear reactions in the domain of quasideuteron absorption and at higher photon energies. It was demonstrated that due to the presence of a single heavy residue in the final state mostly accompanied by free protons and neutrons, the cross sections of the production of specific elements can be well approximated by the proton emission cross sections, which can be measured in the ALICE experiment at the LHC.