1s Lamb shift in heavy H-like ions: towards an accuracy of <1eV

The Rapid Reaction Task Force “1s Lamb shift in heavy H-like ions: towards an accuracy of <1 eV” is aiming to define the strategy for future experiments at the GSI/FAIR storage rings addressing the 1s Lamb shift in heaviest hydrogen-like ions, such as U91+. In particular, we would like to focus on prioritization of two, up to now complementary, spectroscopic methods: transmission crystal-spectrometers (FOCAL) and micro-calorimeters. Due to the recent success of the FOCAL setup in studying the Lyman centroid energies in H-like Au, a much clearer picture about the role of systematic uncertainties has been obtained which needs to be considered. At the same time, the technology related to micro-calorimeters is substantially progressing. However, a stable performance over weeks for high-precision x-ray spectroscopy as it is required for 1s Lamb Shift experiments appears to be still challenging and demanding. Nevertheless, taking into account the required beam times but also the required resources, a decision about a focused strategy appears to be needed.