Narrow Results

High-precision laser spectroscopy of atomic energy levels enables the measurement of nuclear properties. Sensitivity to these properties is particularly enhanced in muonic atoms which are bound systems of a muon and a nucleus. Exemplary is the measurement of the proton charge radius from muonic hydrogen performed by the CREMA collaboration which resulted in an order of magnitude more precise charge radius as extracted from other methods but at a variance of 7 standard deviations. Here, we summarize the role of muonic atoms for the extraction of nuclear charge radii, we present the status of the so called “proton charge radius puzzle”, and we sketch how muonic atoms can be used to infer also the magnetic nuclear radii, demonstrating again an interesting interplay between atomic and particle/nuclear physics.

A theoretical method based on energy-density-functional theory and quasiparticle-phonon model is applied for investigations of low-energy excitations of different multipolarities in stable and exotic nuclei. Of special interest is the possible relation of these modes to neutron or proton skins.

From investigations of low-energy dipole and quadrupole states new modes of excitations related to pygmy dipole and pygmy quadrupole resonances of neutron or proton character are identified. The astrophysical relevance of the pygmy resonances is discussed.