Long-lived atomic and nuclear states explored using dielectronic recombination

Long-lived atomic or nuclear states are fascinating candidates for investigation and improving our understanding of transition dynamics. The hindered decay modes of metastable species are often accompanied by exotic decay pathways and/or higher order or multi-photon transitions. As a consequence of long lifetimes and extraordinary decay properties, nuclear isomers as well as atomic metastable ions play an important role in astrophysics, for precision spectroscopy, for the study of fundamental symmetries, for energy storage or —based on their small natural widths— for applications as clocks. Storage rings provide a very clean environment with wellcontrolled experimental conditions for the investigation of long-lived species. Our approach for studying metastable states exploits the unique properties of the resonant process of dielectronic recombination (DR) as a spectroscopic tool. DR resonance spectra feature unique signatures associated with the long-lived excited states. Atomic metastable states show up in the DR pattern as new resonance series that originate from the initially metastable configurations. Nuclear isomeric states exhibit resonance fingerprints in the DR spectra mainly due to the distinctively different hyperfine interaction and nuclear size shifts of nuclear ground and isomeric states. In the last two years, our collaboration at the ESR storage ring has achieved substantial progress