Low-energy tests of Delbr\"uck scattering

TL;DR

This paper theoretically investigates Delbruck scattering of photons off atomic targets, focusing on how it can be detected in current synchrotron experiments through changes in angular distribution and polarization.

Contribution

It provides detailed calculations demonstrating the potential observability of Delbruck scattering effects at energies below pair creation thresholds in modern experiments.

Findings

Delbruck scattering causes measurable shifts in photon angular distribution.

Polarization of scattered photons is affected by Delbruck scattering.

Detectability of Delbruck scattering in current experiments is feasible.

Abstract

We present a theoretical study of elastic photon scattering by atomic targets. This process is of special interest since various channels from atomic and nuclear physics as well as quantum elctrodynamics (QED) contribute to it. In this work, we focus on Delbr\"uck scattering which proceeds via production of virtual $e^+e^-$ pairs. In particular, we explore whether and how the Delbr\"uck channel can be "seen" in present synchrotron experiments which employ strongly linearly polarized light in the energy range of a few hundred keV. In order to answer this question, detailed calculations have been performed for the scattering of 300 keV and 889.2 keV photons off helium-like tin ions. Based on these calculations, we argue that the Delbr\"uck scattering for the energies below the threshold for $e^+e^-$ pair creation leads to a shift in the angular distribution and the polarization of the scattered photons which can be observed by state-of-the-art solid-state detectors.