Lamb-Shift experiments on high-Z one-electron ions

One of the most sensitive experimental approaches for the investigation of the effects of quantum electrodynamics in strong Coulomb fields is a precise determination of the ground state energies in high-Z one-electron systems. Similar investigations for low-Z ions are primarily sensitive to the lowest-order self-energy corrections. The study of the higher-order self-energy and vacuum polarization contributions, however, requires the heaviest ions available. Here, the goal of the experiments is to probe higher-order QED contributions which correspond to Feynman diagrams such as the two-photon exchange diagrams. For the case of uranium, where the total 1s Lamb shift contributes 464 eV to the total ground state binding energy of 131.816 keV, a stringent test of QED requires an absolute experimental accuracy of about ± 1 eV which represents the accuracy theoreticans claim presently. For such studies the ESR storage ring provides favorable experimental conditions. This has been demonstrated within the first series of experiments performed at the ESR gas jet target as well as at the electron cooler device. For the case of the 1s-Lamb shift in hydrogen-like uranium, the achieved accuracy of ±13 eV is already a substantial improvement by almost one order of magnitude compared to a former experiment conducted at the BEVALAC accelerator.