The Pygmy Dipole Resonance-status and new developments

Abstract

At energies well below the isovector electric Giant Dipole Resonance, a concentration of electric dipole strength is observed in many stable and radioactive nuclei. This low-lying excitation mode is usually denoted as Pygmy Dipole Resonance (PDR). Different theoretical approaches can reproduce the gross features, like the energetic position and partly the excitation strength of the PDR, but they differ considerably in its underlying structural description. More sophisticated experiments looking for the isospin character, the detailed decay pattern, and the single-particle structure of the low-lying E1 excitations are therefore mandatory to gain a deeper understanding. This manuscript will give an overview about the most recent experimental results and present new experimental tools for the future.