Large contribution of virtual Delbrueck scattering to the emission of photons by relativistic nuclei in nucleus-nucleus and electron-nucleus collisions

TL;DR

This paper investigates how virtual Delbrueck scattering significantly contributes to photon emission in ultra-relativistic nucleus-nucleus and electron-nucleus collisions, with large cross sections at collider energies.

Contribution

It quantifies the impact of virtual Delbrueck scattering on photon emission, revealing it dominates over traditional bremsstrahlung in high-energy nuclear collisions.

Findings

Cross section of 14 barns for Au-Au at RHIC

Cross section of 50 barns for Pb-Pb at LHC

No infrared divergence in the process

Abstract

Delbrueck scattering is an elastic scattering of a photon in the Coulomb field of a nucleus via a virtual electron loop. The contribution of this virtual subprocess to the emission of a photon in the collision of ultra-relativistic nuclei Z_1 Z_2 -> Z_1 Z_2 gamma is considered. We identify the incoming virtual photon as being generated by one of the relativistic nuclei involved in the binary collision and the scattered photon as being emitted in the process. The energy and angular distributions of the photons are calculated. The discussed process has no infrared divergence. The total cross section obtained is 14 barn for Au-Au collisions at the RHIC collider and 50 barn for Pb-Pb collisions at the LHC collider. These cross sections are considerably larger than those for ordinary tree-level nuclear bremsstrahlung in the considered photon energy range m_e << E_\gamma << m_e gamma, where gamma is the Lorentz factor of the nucleus. Finally, photon emission in electron-nucleus collisions e Z -> e Z gamma is discussed in the context of the eRHIC option.