Background Field Effects on Quasi-Real Photon Emission and Lepton-Pair Production at EIC and EicC

TL;DR

This paper investigates how background electromagnetic fields influence quasi-real photon emission and lepton-pair production at EIC and EicC, revealing non-negligible corrections that affect gluon distribution measurements.

Contribution

It introduces a non-perturbative correction to the photon propagator due to background fields, impacting photon flux and gluon distribution extraction.

Findings

Background fields modify photon flux spectrum.

Corrections are significant in certain kinematic regions.

Impacts on small-x gluon distribution extraction.

Abstract

We study how background electromagnetic fields modify quasi-real photon emission at the EIC and EicC through an effective coupling correction, thereby altering the photon flux spectrum. The resulting change in lepton-pair production via photon-photon fusion, where one photon arises from the electron and the other from the nuclear Coulomb field-serves as a clean QED probe of such background effects. In our formulation, the correction originates from a non-perturbative modification of the photon propagator induced by the background field. Because this process shares the same initial-state photon dynamics as photon-gluon fusion, any background-induced alteration of the photon propagator directly impacts the extraction of small-$x$ gluon distributions. Numerical estimates at realistic collider energies indicate that these corrections should be non-negligible in certain kinematic regions.