Angular modulation of nonlinear Breit-Wheeler yield by vacuum dichroism

TL;DR

This paper investigates how vacuum dichroism influences the nonlinear Breit-Wheeler process in ultraintense laser interactions, revealing that vacuum polarization effects can be detected via pair yield modifications in a straightforward experimental setup.

Contribution

It introduces a novel method to observe vacuum polarization effects through pair yield changes without requiring polarized probe photons or precise polarization measurements.

Findings

Vacuum dichroism enhances linear photon polarization purity.

It suppresses overall electron-positron pair yield.

Energetic photons penetrate deeper, increasing forward pair production.

Abstract

Vacuum polarization is numerically investigated for the interaction between a GeV electron beam and a counterpropagating ultraintense laser pulse in the quantum radiation dominated-regime (QRDR). We identify a signal of vacuum polarization in pair density using a straightforward one-stage setup, circumventing the challenge of preparations of highly polarized probe photons or precise measurements of photon polarization. In our scheme, most electrons are scattered in the direction of laser propagation while emitting substantial linearly polarized gamma photons. These photons undergo vacuum birefringence and dichroism before decaying into electron-positron pairs via the nonlinear Breit-Wheeler process. We demonstrate that vacuum dichroism enhances the purity of linear polarization, which suppresses the overall yield of electron-positron pairs and allows energetic photons to penetrate deeper into the laser pulse. The pairs produced by these energetic photons are more likely to be deflected into small-angle regions rather than being reflected, leading to an enhancement of pair yield in forward scattering. The difference in positron yield may have potential applications in measuring vacuum polarization effect in future laser-particle experiments.