$1\mathit{s}$ Lamb Shift in Hydrogenlike Uranium Measured on Cooled, Decelerated Ion Beams

The Lyman- $\alpha$ transitions of hydrogenlike uranium associated with electron capture were measured in collisions of stored bare $\mathrm{U}{}^{92+}$ ions with gaseous targets at the storage ring ESR. By applying the deceleration technique, the experiment was performed at slow collision energies in order to reduce the uncertainties associated with Doppler corrections. From the measured centroid energies, a ground state Lamb shift of $468\mathrm{eV}\pm 13\mathrm{eV}$ is deduced which gives the most precise test of quantum electrodynamics for a single electron system in the strong field regime. In particular, the technique applied paves the way towards the 1 eV precision regime.