2025/04/10 by ATLAS Collaboration · 2 citations
#FOS: Physical sciences #High Energy Physics - Experiment (hep-ex) #Nuclear Experiment (nucl-ex)
paper · doi:10.48550/arxiv.2504.07795
The Lorentz-contracted electromagnetic fields of the ions in ultra-relativistic heavy-ion collisions generate intense quasi-real photon fluxes. These lead to photon-induced interactions that are observed in ultra-peripheral collisions (UPCs), such as vector meson and lepton-pair production. The high photon flux also enables the occurrence of multiple photon-induced processes in a single collision. Presented is the first measurement of the coincident production of γγ→ μ+μ- and γ+A→ρ0+A in UPC Pb+Pb collisions at centre-of-mass energies of 5.02 TeV and 5.36 TeV with the ATLAS detector at the Large Hadron Collider. The rate of the coincident process relative to the exclusive γγ→ μ+μ- process is measured differentially in intervals of forward event activity, quantified by the Zero Degree Calorimeters. The relative rate, summed over forward event activity, for the coincident ρ0 production is measured to be (9.3 ±0.4 (stat.) ±0.2 (syst.))×10-3. Correlations between the dimuon kinematic properties, such as its mass, and the coincident ρ0 meson production rate, are also presented. These measurements confirm the presence of multi photon-induced processes in UPC collisions, and can provide new insight into the impact parameter dependence of photon-induced vector meson production.