First Experiments Aiming for Precise Lamb Shift Measurements on Hydrogen-Like Heavy Ions with Low Temperature Calorimeters

Abstract

The precise determination of the Lamb shift in hydrogen-like heavy ions provides a sensitive test of quantum electrodynamics in very strong Coulomb fields, not accessible otherwise. To increase the accuracy of the Lamb shift measurement on stored heavy ions at the ESR storage ring at GSI, a calorimetric low temperature detector for hard X-rays was developed. A prototype array consisting of 8 pixels with silicon thermistors and Sn or Pb absorbers was applied in first experiments with stored 238U91+ and 207Pb81+ ions interacting with an internal gas-jet target. In both experiments the Lyman-α lines were, for the first time by using calorimetric low temperature detectors, clearly identified in clean, almost background-free spectra. A total detection efficiency of 1×10−7 for the Lyman-α lines was reached and an energy resolution of 115 eV was obtained under the present experimental conditions, which corresponds to a considerable improvement of about half an order of magnitude if compared to conventional Ge semiconductor detectors. Finally preliminary results of the data analysis and future perspectives are discussed.