Quantum Electrodynamics in Strong Electromagnetic Fields: Substate Resolved K$\alpha$ Transition Energies in Helium-like Uranium

TL;DR

This study used advanced detectors to precisely measure Kα transition energies in helium-like uranium, confirming strong-field QED predictions and resolving previous experimental-theoretical discrepancies.

Contribution

First high-resolution measurement of Kα transition energies in helium-like uranium confirming theoretical predictions in strong electromagnetic fields.

Findings

Good agreement with QED calculations

No systematic deviation between experiment and theory

Enhanced spectral resolution achieved

Abstract

Using novel metallic magnetic calorimeter detectors at the CRYRING@ESR, we recorded X-ray spectra of stored and electron cooled helium-like uranium (U$^{90+}$) with an unmatched spectral resolution of close to 90 eV. This allowed for an accurate determination of the energies of all four components of the K$\alpha$ transitions in U$^{90+}$. We find good agreement with state-of-the-art bound-state QED calculations for the strong-field regime. Our results do not support any systematic deviation between experiment and theory in helium-like systems, the presence of which was subject of intense debates in recent years.