Isospin symmetry breaking in mirror nuclei

Isospin symmetry is one of the fundamental symmetries we can identify in nuclei. This is related to the approximate charge symmetry and charge independence of the strong interaction. On this hypothesis, the level schemes of mirror nuclei (with exchanged number of protons and neutrons) should be identical. Of course some differences appear due to the fact that the Coulomb interaction breaks isospin symmetry. Energy differences between excited states in mirror nuclei can therefore be explained to a large extent in terms of the Coulomb effects. Recent investigations, however, suggest the need to introduce a non-Coulomb isospin symmetry breaking term to get a satisfactory quantitative description of the available data. In the last decade or so, the study of energy differences in isobaric nuclei as a function of angular momentum has been done systematically for nuclei in the f 7 2 shell. This has been possible due to important experimental developments in the identification of proton-rich nuclei produced with very low cross sections. Contemporaneously, state-of-the-art shell-model calculations have been produced for the description of these data. The synergy between theory and experiment for the study of energy differences of mirror and isobaric analogue nuclei has allowed the investigation of the evolution of the nuclear wave functions with increasing spin. The alignment process, related to changes of the spatial correlations of nucleons along a rotational band, together with changes of the nuclear radius or shape as a function of the angular momentum are examples of the type of phenomena that can be studied from the analysis of Coulomb energy differences. It is also possible to identify particular wave-function configurations of the states. In summary, the study of mirror energy differences has now become established as a very powerful tool to understand nuclear properties in nuclei. While most of the investigations so far have been concentrated mainly in nuclei of the f 7 2 shell, extensions to other shells are becoming available, which allows us to develop a more general view and description of the different properties that can be deduced from the data.