QED effects in lithiumlike krypton

The (2s(1/2)-2p(1/2)) Lamb shift in lithiumlike krypton was obtained through a recombination measurement. The Lamb shift was extracted from the recombination spectrum by comparison with a calculation of the dielectronic-recombination resonance positions. The energy calibration used in this work is based on an accurate energy determination of one arbitrary point in the spectrum. Our value for the 2s(1/2)-2p(1/2) energy difference is 71.243(8) eV. The relativistic many-body contributions to the Lamb shift can be calculated very precisely, which enabled an extraction of an experimental'' quantum-electrodynamical contribution of 1.539(8) eV. This precision is beyond what can be achieved with conventional estimates of the screened quantum-electrodynamical effects. The main error originates from the uncertainty in the length of the ion-beam orbit. Improved knowledge of this value can improve our result significantly.