The Lamb shift in hydrogen and muonic hydrogen and the proton charge radius
Dr. Savely Karshenboim (MPI für Quantenoptik, Garching)

Some time ago evaluations of electron-proton-scattering data were consistent with a value of the proton charge radius obtained from hydrogen spectroscopy. The value has been seen as a clean and reliable one, but only until a recent PSI experiment on muonic hydrogen delivered its first results.

Study of the Lamb shift in muonic hydrogen is potentially the most accurate way to determine the proton charge radius comparing with methods applied previously. However, there is a 5 sigma discrepancy between muonic and conventional values.

Precision theory of the atomic energy levels is bound-state quantum electrodynamics. Such a theory deals with a somewhat simplier contributions than theory of the anomalous magnetic moment of an electron and muon, but it has specitic complicity because of bound state nature of atomic levels.

The state of the art in muonic-hydrogen and hydrogen Lamb shift and in proton charge radius determination will be presented as well as basics of bound state QED theory.