Precision Study of the 1s Lamb Shift in Heavy Ions

Atomic systems with a single bound electron “circling” a heavy nucleus such as lead or uranium constitute an extreme state of matter, forming the prototype for investigations of QED in strong fields. At the ESR heavy ion storage ring at GSI, recently a high-precision experiment to determine the 1s Lamb shift in heavy, hydrogen-like gold (Au⁷⁸⁺) was conducted. Using the FOCAL crystal spectrometer, at about 60 keV X-ray energy a measurement error of 1 eV was aimed for (data evaluation currently in progress). This degree of accuracy puts QED in strong fields to an extremely rigorous test.