From charge to magnetic radii

We have measured several 2S-2P transitions in muonic hydrogen (µp), muonic deuterium (µd) and muonic helium ions (µ³He, µ⁴He). From muonic hydrogen we extracted a proton charge radius 20 times more precise than obtained from electron-proton scattering and hydrogen high-precision laser spectroscopy but at a variance of 7 Sigma from these values. This discrepancy is nowadays referred to as the „proton radius puzzle". The status of the proton charge radius puzzle including the new insights obtained by µd spectroscopy will be discussed in the first part of this contribution. The second part will be devoted to the new activities at PSI related with spectroscopy of muonic atoms which include measurements of the ground state hyperfine splitting in µp and µ³He as well as activities related with high-Z muonic atoms. Zemach radii and eventually information about the magnetic radii can be extracted from the hyperfine splitting measurements. High-Z atoms spectroscopy provides nuclear charge radii to test many-body nuclear theories and are motivated also by atomic parity violation searches.