Microscopic nuclear form factor for the pygmy dipole resonance

E.G Lanza,F Catara,M.V Andrés,A Vitturi

doi:10.1051/epjconf/201611706017

Abstract

Pygmy dipole resonance can be populated via isoscalar probes due to the strong mixing of isoscalar and isovector components. The physical quantities are usually extracted by the use of reaction theory calculations. There, the most important ingredient is the form factor which contains all the relevant properties of the states we are dealing with. We show that the use of microscopic form factor is required for a better analysis of experimental results.

Highlights

Among the most interesting new phenomena related to the nuclei with neutron excess, the low lying dipole states [1,2,3], known as Pygmy Dipole Resonance (PDR), acquired a special role for its connections with other branch of physics
All of these calculations show similar behaviors for the transition densities: the neutron and proton ones are in phase inside the nucleus while at the surface only the neutron part contributes significantly. This feature generates a strong mixing of isospin character and even an isoscalar probe can be used to explore these low lying dipole states
10-20 r transition densities of fig.2. Such conditions has the typical shape of the compressional modes. There is another way to calculate a transition density based on the common picture that one has in mind about the nature of the PDR mode

Summary

Introduction

Among the most interesting new phenomena related to the nuclei with neutron excess, the low lying dipole states [1,2,3], known as Pygmy Dipole Resonance (PDR), acquired a special role for its connections with other branch of physics. PDR states are better described within microscopic self consistent manybody approaches or on the relativistic meson-exchange Lagrangian [1] All of these calculations show similar behaviors for the transition densities: the neutron and proton ones are in phase inside the nucleus while at the surface only the neutron part contributes significantly. This feature generates a strong mixing of isospin character and even an isoscalar probe can be used to explore these low lying dipole states. Most of the physical information obtained by using isoscalar probes depend on how well the nuclear properties of the state under investigation are described within the radial form factors. Full details can be found in ref. [16]

Transition densities and nuclear form factors

Conclusion