Low-lying magnetic excitations of doubly-closed-shell nuclei and nucleon-nucleon effective interactions

TL;DR

This study investigates low-lying magnetic excitations in doubly-closed-shell nuclei using RPA theory, revealing that accurate modeling constrains the spin and tensor components of nucleon-nucleon interactions, with implications for effective interaction validity.

Contribution

The paper demonstrates how magnetic spectra analysis constrains effective nucleon-nucleon interactions and tests the Gogny D1 interaction's validity in describing magnetic states.

Findings

Good agreement with experimental spectra using phenomenological interactions

Gogny D1 interaction inverts energies of magnetic isospin doublets

Magnetic spectra impose constraints on spin and tensor terms

Abstract

We have studied the low lying magnetic spectra of 12C, 16O, 40Ca, 48Ca and 208Pb nuclei within the Random Phase Approximation (RPA) theory, finding that the description of low-lying magnetic states of doubly-closed-shell nuclei imposes severe constraints on the spin and tensor terms of the nucleon-nucleon effective interaction. We have first made an investigation by using four phenomenological effective interactions and we have obtained good agreement with the experimental magnetic spectra, and, to a lesser extent, with the electron scattering responses. Then we have made self-consistent RPA calculations to test the validity of the finite-range D1 Gogny interaction. For all the nuclei under study we have found that this interaction inverts the energies of all the magnetic states forming isospin doublets.