Precise Lamb Shift Measurements in Hydrogen-Like Heavy Ions—Status and Perspectives

Abstract

The precise determination of the energy of the Lyman α1 and α2 lines in hydrogen‐like heavy ions provides a sensitive test of quantum electrodynamics in very strong Coulomb fields. For the first time, a calorimetric low‐temperature detector was applied in an experiment to precisely determine the transition energy of the Lyman lines of lead ions 207pb81+ at the Experimental Storage Ring (ESR) at GSI. The detectors consist of silicon thermistors, provided by the NASA/Goddard Space Flight Center, and Pb or Sn absorbers to obtain high quantum efficiency in the energy range of 40–80 keV, where the Doppler‐shifted Lyman lines are located. The measured energy of the Lyman α1 line, E(Ly‐α1, 207Pb81+) = (77937±12stat±23syst) eV, agrees within errors with theoretical predictions. The systematic error is mainly due to uncertainties in the non‐linear energy calibration of the detectors as well as the relative position of detector and gas‐jet target.