Testing Strong-Field QED to Second Order in the Highly Correlated Atomic System Berylliumlike Pb78+ by Electron-Ion Collision Spectroscopy

Schippers S; others

Abstract

A low-energy storage ring with an ultracold electron cooler has been coupled with a heavy-ion accelerator facilitating high-resolution electron-ion collision spectroscopy of the heaviest few-electron ions. In the present Letter resonant electron-ion recombination of berylliumlike Pb78+ ions was measured in the collision-energy range 9.3–16.5 eV and a value of 244.937(30) eV is derived for the Pb78+⁢(2⁢𝑠2 1𝑆0−2⁢𝑠⁢2⁢𝑝 3𝑃1) excitation energy. This result agrees with the most recent (less accurate) theoretical value of 244.942(52) eV [Malyshev et al., Phys. Rev. A 110, 062824 (2024)], which has been calculated by applying strong-field QED rigorously up to the second order. The present investigation suggests that further technical improvements can potentially increase the experimental accuracy by an order of magnitude.