Structure of the Pygmy Dipole Resonance

• Applicant: Professor Dr. Andreas Zilges
• Subject Area: Nuclear and Elementary Particle Physics, Quantum Mechanics, Relativity, Fields
• Term: from 2014 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 261863245

Many properties of atomic nuclei can be described by the assumption of a symmetric behavior of its two constituents, the protons and neutrons. Therefore, electric dipole excitations of the nucleus are an interesting observable, since they require a breaking of the proton-neutron symmetry. The electric dipole response of a nucleus is dominated by the Giant Dipole Resonance (GDR) which lies at relatively high excitation energy and can be described as an out-of-phase oscillation of all neutrons against all protons. Recently the discovery of substantial electric dipole strength at much lower excitation energy in certain nuclei has attracted a lot of interest. These excitations are often denoted as Pygmy Dipole Resonance (PDR). The study of the PDR is not only relevant for nuclear structure physics, but can as well have an impact on the symmetry energy term in the equation of state, and on the synthesis of heavy nuclei.Within the proposed research project we plan to complete our presently very fragmentary knowledge about the PDR to allow stringent test of theoretical descriptions. Major open question we want to address are the decay properties of the excitations, a possible splitting into a dominantly isoscalar and a dominantly isovector component, and the underlying single particle structure. For this purpose we plan experiments at different setups in Germany and abroad. The experiments will be closely accompanied by theoretical calculations.

• DFG Programme: Research Grants