Probing the Collision Geometry via Two-Photon Processes in Heavy-Ion Collisions

TL;DR

This paper demonstrates that dilepton production via two-photon processes in heavy-ion collisions can serve as a novel probe of the initial collision geometry, leveraging photon polarization correlations to improve understanding of quark-gluon plasma characteristics.

Contribution

It introduces a QED-based method to use two-photon dilepton production as a polarization-sensitive probe of collision geometry in heavy-ion experiments.

Findings

Dilepton emission angles are sensitive to collision geometry.

The approach provides a new way to quantify initial collision conditions.

Results are applicable at RHIC and LHC energies.

Abstract

The initial collision geometry, including the reaction plane, is crucial for interpreting collective phenomena in relativistic heavy-ion collisions, yet it remains experimentally inaccessible through conventional measurements. Recent studies propose utilizing photon-induced processes as a direct probe, leveraging the complete linear polarization of emitted photons whose orientation strongly correlates with the collision geometry. In this work, we employ a QED-based approach to systematically investigate dilepton production via two-photon processes in heavy-ion collisions at RHIC and LHC energies and detector acceptances. Our calculations reveal that dilepton emission exhibits significant sensitivity to the initial collision geometry through both the azimuthal angles of their emission (defined by the relative momentum vector of the two leptons) and the overall momentum orientation of the dilepton pairs. These findings highlight the potential of two-photon-generated dileptons as a novel, polarization-driven probe to quantify the initial collision geometry and reduce uncertainties in characterizing quark-gluon plasma properties.