Direct accessibility of the fundamental constants governing light-by-light scattering

TL;DR

This paper proposes a novel experimental setup to directly measure the fundamental constants of light-by-light scattering, leveraging high-intensity lasers and x-ray probes, enabling precise quantum vacuum studies.

Contribution

It introduces a new experimental approach that suppresses background noise, allowing direct and precise measurement of the constants governing light-by-light scattering.

Findings

Background suppression by several orders of magnitude.

Detection of the perpendicular polarisation component of vacuum response.

Potential for first-time measurement of the parallel polarisation component.

Abstract

Quantum field theory predicts the vacuum to exhibit a non-linear response to strong electromagnetic fields. This fundamental tenet has remained experimentally challenging and is yet to be tested in the laboratory. We present proof of concept and detailed theoretical analysis of an experimental setup for precision measurements of the quantum vacuum signal generated by the collision of a brilliant x-ray probe with a high-intensity pump laser. The signal features components polarised parallel and perpendicularly to the incident x-ray probe. Our proof-of-concept measurements show that the background can be efficiently suppressed by many orders of magnitude which should not only facilitate a detection of the perpendicularly polarised component of non-linear vacuum response, but even make the parallel polarised component experimentally accessible for the first time. Remarkably, the angular separation of the signal from the intense x-ray probe enables precision measurements even in presence of pump fluctuations and alignment jitter. This provides direct access to the low-energy constants governing light-by-light scattering.