Electromagnetic interaction of low transverse momentum electrons and positrons with heavy nuclei in ultra-peripheral ultra-relativistic heavy-ion collisions

TL;DR

This paper investigates how electromagnetic interactions affect low transverse momentum electron-positron pairs produced in ultra-peripheral heavy-ion collisions, revealing significant distortions in their distributions at SPS and RHIC energies.

Contribution

It provides the first detailed calculations of electromagnetic effects on lepton distributions in ultra-peripheral heavy-ion collisions using the b-space EPA model.

Findings

Strong electromagnetic effects at low transverse momenta.

Predicted asymmetry in electron and positron production.

Potential accumulation of electrons near beam rapidity.

Abstract

The photon-photon interaction in ultra-relativistic heavy-ion collision is a source of the $(e^+,e^-)$ pairs. The photon-photon fusion leads the lepton creation in the broad configuration space around "collision" point. Those created close to heavy nuclei may undergo strong interaction with them. The impact parameter space distribution of electrons and positrons are calculated within the b-space EPA model of such collisions. The evolution due to the electromagnetic interaction of $(e^+,e^-)$ with nuclei is studied, and the distortion of rapidity and transverse momentum distributions are shown. We show first exploratory results for the reaction Pb+Pb at $\sqrt{s_{NN}}=$ 17.3 GeV (SPS) and 200 GeV (RHIC) energies. We provide results for selected creation points and when integrating over their position as dictated by the $b$-space EPA model. We observe strong effects at low transverse momenta, so far not measured regions of the phase space. In particular, we predict a possible sizeable accumulation of electrons with rapidities close to the beam rapidity. The EM effects lead to asymmetry in the production of electrons and positrons.