Dipole response in 208Pb within a self-consistent multiphonon approach

Abstract

Background: The electric dipole strength detected around the particle threshold and commonly associated to the pygmy dipole resonance offers a unique information on neutron skin and symmetry energy, and is of astrophysical interest. The nature of such a resonance is still under debate. Purpose: We intend to describe the giant and pygmy resonances in 208 Pb by enhancing their fragmentation with respect to the random-phase approximation. Method: We adopt the equation of motion phonon method to perform a fully self-consistent calculation in a space spanned by one-phonon and two-phonon basis states using an optimized chiral two-body potential. A phenomenological density dependent term, derived from a contact three-body force, is added in order to get single-particle spectra more realistic than the ones obtained by using the chiral potential only. The calculation takes into full account the Pauli principle and is free of spurious center of mass admixtures. Results: We obtain a fair description of the giant resonance and obtain a dense low-lying spectrum in qualitative agreement with the experimental data. The transition densities as well as the phonon and particle-hole composi- tion of the most strongly excited states support the pygmy nature of the low-lying resonance. Finally, we obtain realistic values for the dipole polarizability and the neutron skin radius. Conclusions: The results emphasize the role of the two-phonon states in enhancing the fragmentation of the strength in the giant resonance region and at low energy, consistently with experiments. For a more detailed agreement with the data, the calculation suggests the inclusion of the three-phonon states as well as a fine tuning of the single-particle spectrum to be obtained by a refinement of the nuclear potential.

13 pages, 10 figures

References in corpus (17)

• Chiral effective field theory and nuclear forces
• Exotic modes of excitation in atomic nuclei far from stability
• Accurate nuclear radii and binding energies from a chiral interaction
• Constraints on the symmetry energy and on neutron skins from the pygmy resonances in 68Ni and 132Sn
• Pygmy dipole resonance as a constraint on the neutron skin of heavy nuclei
• Isospin Character of the Pygmy Dipole Resonance in 124Sn
• Investigation of Pygmy Dipole Resonances in the Tin Region
• Pygmy Resonances and Neutron Skins
• Relativistic quasiparticle time blocking approximation. Dipole response of open-shell nuclei
• Self-consistent description of multipole strength: systematic calculations
• Fragmentation and systematics of the Pygmy Dipole Resonance in the stable N=82 isotones
• Relativistic RPA plus phonon-coupling analysis of pygmy dipole resonances
• Microscopic linear response calculations based on the Skyrme functional plus the pairing contribution
• Low-energy dipole excitations in neon isotopes and N=16 isotones within the quasiparticle random phase approximation and the Gogny force
• A self-consistent study of multipole response in neutron-rich nuclei using a modified realistic potential
• Quasiparticle Random Phase Approximation with Interactions from the Similarity Renormalization Group
• The quest for novel modes of excitation in exotic nuclei

Cited by in corpus (7)

• Nuclear Equation of State from ground and collective excited state properties of nuclei
• Dipole response in neutron-rich nuclei with new Skyrme interactions
• Nuclear Shell Structure in a Finite-Temperature Relativistic Framework
• Sensitivity of Λ single-particle energies to the ΛN spin-orbit coupling and to nuclear core structure in p-shell and sd-shell hypernuclei
• Temperature evolution of the nuclear shell structure and the dynamical nucleon effective mass
• Daejeon16 interaction with contact-term corrections for heavy nuclear systems
• Effect of a realistic three-body force on the spectra of medium-mass hypernuclei