Vacuum birefringence and diffraction at XFEL: from analytical estimates to optimal parameters

TL;DR

This paper provides analytical estimates and optimal parameter strategies for detecting vacuum birefringence and photon scattering at XFEL facilities, crucial for future experimental discovery.

Contribution

It introduces new analytical scalings and optimized approximations for signal photon counts, enhancing experimental design for vacuum birefringence detection.

Findings

Analytical approximations achieve 1% accuracy.

Optimal focus and pulse duration significantly increase signal.

Application to European XFEL parameters demonstrates feasibility.

Abstract

We study vacuum birefringence and x-ray photon scattering in the head-on collision of x-ray free electron and high-intensity laser pulses. Resorting to analytical approximations for the numbers of attainable signal photons, we analyze the behavior of the phenomenon under the variation of various experimental key-parameters and provide new analytical scalings. Our optimized approximations allow for quantitatively accurate results on the one-percent level. We in particular demonstrate that an appropriate choice of the x-ray focus and pulse duration can significantly improve the signal for given laser parameters, using the experimental parameters to be available at the Helmholtz International Beamline for Extreme Fields at the European XFEL as example. Our results are essential for the identification of the optimal choice of parameters in a discovery experiment of vacuum birefringence at the high-intensity frontier.