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Pygmy dipole resonances in relativistic random phase approximation

D. Vretenar·N. Paar·P. Ring·G. A. Lalazissis
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Abstract

The isovector dipole response in $^{208}$Pb is described in the framework of a fully self-consistent relativistic random phase approximation. The NL3 parameter set for the effective mean-field Lagrangian with nonlinear meson self-interaction terms, used in the present calculations, reproduces ground state properties as well as the excitation energies of giant resonances in nuclei. In addition to the isovector dipole resonance in $^{208}$Pb, the present analysis predicts the occurrence of low-lying E1 peaks in the energy region between 7 and 11 MeV. In particular, a collective state has been identified whose dynamics correspond to that of a dipole pygmy resonance: the vibration of the excess neutrons against the inert core composed of equal number of protons and neutrons.

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D. Vretenar, N. Paar, P. Ring, G. A. Lalazissis. 2000-09-21. Pygmy dipole resonances in relativistic random phase approximation. https://doi.org/10.1103/physrevc.63.047301

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