Experimental Developments for the Lamb Shift Investigation in Heavy Ions (abstract)

Novel high‐resolution spectrometer setups are presently commissioned for X‐ray experiments at the Experimental Storage Ring (ESR) at GSI, Darmstadt, aiming at an accurate determination of QED corrections in the critical field limit via an accurate determination of the ground‐state binding energy in a high‐Z, H‐like ion. Until now for H‐like uranium, an accuracy of 1% could be reached in an experiment performed at the electron cooler, due to the deceleration capability of the ESR. A further improvement by almost one order of magnitude is envisaged by a transmission x‐ray spectrometer setup in the FOcusing Compensated Asymmetric Laue (FOCAL) geometry, as well as by the implementation of high‐resolution microcalorimeter devices.Here we report on the latest commissioning experiment of a two‐arm transmission X‐ray spectrometer, along with high‐performance position‐sensitive microstrip germanium detectors. Due to a photon efficiency of only 10−8, the position sensitivity, as well as the energy and time resoluti...