The electron screening effect in muonic 28Si

Abstract We have measured the wavelengths of the 4 f 7 2 -3 d 5 2 and the 4 f 5 2 -3 d 3 2 X-ray transitions in μ- 28 Si with the bent-crystal spectrometer at the SIN muon channel. The results are compared to the calculated transition wavelengths which include radiative corrections (QED). The differences in the corresponding transition energies are attributed to the electron screening shift. Combining the results from both transitions, we obtain ΔE ES (4f-3d) = −1.66±0.20 eV. This corresponds to (83±11)% of the electron-screening shift calculated for a neutral atom with the muon and Z − 1 electrons. These results are in moderate agreement with cascade calculations constrained to reproduce measured muonic X-ray intensities.