Pygmy dipole resonances in relativistic random phase approximation

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.

LaTex 7 pages, 4 eps Figs, submitted to Phys. Lett. B

References in corpus (1)

• Isoscalar dipole mode in relativistic random phase approximation

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