What question did this study set out to answer?

This research aims to analyze the interactions of photons in heavy ion collisions and their impact on vector meson production.

April 22, 2026

Measurements of

Key Points

This research aims to analyze the interactions of photons in heavy ion collisions and their impact on vector meson production.
Utilized a low-multiplicity track trigger in the ATLAS experiment during Run 3.
Collected a large sample of events focused on few track configurations.
Assessed coherent J/ψ yields across the continuous rapidity range at the LHC.
Presented first results on coherent J/ψ yields from heavy ion collisions.
Found significant effects from multiple ultra-peripheral collision (UPC) processes.
Demonstrated sensitivity of exclusive vector mesons to nuclear parton distribution functions.

Abstract

The fully stripped ions used in heavy ion collisions at the LHC are an excellent source of high-energy quasi-real photons. These can interact with photons emitted by the oncoming nucleus, or with the nucleus itself, either directly in inelastic processes or diffractively via pomeron exchange. Diffractive photonuclear processes can produce exclusive vector mesons that are uniquely sensitive to the spatial and momentum structure of the nuclear parton distribution functions, as well as spatial fluctuations (hotspots). In Run 3, the ATLAS experiment utilized a low-multiplicity track trigger in heavy ions for the first time, allowing the collection of a large sample of events with a few tracks. A substantial fraction of these are sensitive to dilepton decays of vector mesons, including the J/ψ. First results on coherent J/ψ yields are presented using the widest continuous rapidity range available at the LHC. A discussion of important contributions from multiple-UPC processes is also provided.

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