Logo
ScienceStack
Table of Contents
Fetching ...
Sign In

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

Cong Li

TL;DR

The paper investigates how strong background electromagnetic fields in electron–ion collisions modify initial-state QED via a nonperturbative correction to the photon propagator. An effective coupling $\alpha_{\text{eff}}(k)=\alpha_e[n(k)+1]$ is introduced, and the quasi-real photon flux is modeled with the EPA to recalculate the cross section for $\gamma^*\gamma^* \to \ell^+\ell^-$, including Sudakov resummation. Numerical results for EIC and EicC show enhancements up to about two orders of magnitude in certain $q_\perp$ regions, implying potential biases in small-$x$ gluon distribution extractions if these effects are neglected. The findings emphasize the importance of incorporating background-field QED corrections into precision analyses of photon-initiated processes at future colliders, and guide future work to extend beyond the quasi-real limit, include electron propagator effects, and explore additional observables such as angular correlations and polarization asymmetries.

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.

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

TL;DR

The paper investigates how strong background electromagnetic fields in electron–ion collisions modify initial-state QED via a nonperturbative correction to the photon propagator. An effective coupling is introduced, and the quasi-real photon flux is modeled with the EPA to recalculate the cross section for , including Sudakov resummation. Numerical results for EIC and EicC show enhancements up to about two orders of magnitude in certain regions, implying potential biases in small- gluon distribution extractions if these effects are neglected. The findings emphasize the importance of incorporating background-field QED corrections into precision analyses of photon-initiated processes at future colliders, and guide future work to extend beyond the quasi-real limit, include electron propagator effects, and explore additional observables such as angular correlations and polarization asymmetries.

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- gluon distributions. Numerical estimates at realistic collider energies indicate that these corrections should be non-negligible in certain kinematic regions.

Paper Structure

This paper contains 3 sections, 11 equations, 3 figures.

Table of Contents

  1. Introduction
  2. Correction of coupling constant by background field
  3. Summary and outlook

Figures (3)

  • Figure 1: The effect of the background field on the photon propagator can be equivalently interpreted as a modification to the coupling constant.
  • Figure 2: Differential cross section for the process $e^-+Pb \to e^-+Pb+e^+e^-$ as a function of $q_\perp$ at EicC energies. Left: without the background field effect. Right: with the background field effect. The rapidity of final-state electrons is integrated over the region [1.5, 2].
  • Figure 3: Differential cross section for the process $e^-+Pb \to e^-+Pb+e^+e^-$ as a function of $q_\perp$ at EIC energies. Left: without the background field effect. Right: with the background field effect. The rapidity of final-state electrons is integrated over the region [2, 2.8].