Evolution of the proton sd states in neutron-rich Ca isotopes

TL;DR

This study investigates how proton single-particle states in calcium isotopes evolve with neutron number, revealing sensitivities to neutron shell structure and the influence of tensor interactions on state inversion near $^{48}$Ca.

Contribution

It provides a comparative analysis using non-relativistic and relativistic models, highlighting the impact of tensor forces on proton state inversion in neutron-rich calcium isotopes.

Findings

Proton state energies are sensitive to neutron shell filling.

State inversion near $^{48}$Ca is influenced by tensor interactions.

Both models show similar trends in state evolution.

Abstract

We analyze the evolution with increasing isospin asymmetry of the proton single-particle states 2s1/2 and 1d3/2 in Ca isotopes, using non-relativistic and relativistic mean field approaches. Both models give similar trends and it is shown that this evolution is sensitive to the neutron shell structure, the two states becoming more or less close depending on the neutron orbitals which are filled. In the regions where the states get closer some parametrizations predict an inversion between them. This inversion occurs near $^{48}$Ca as well as very far from stability where the two states systematically cross each other if the drip line predicted in the model is located far enough. We study in detail the modification of the two single-particle energies by using the equivalent potential in the Schroedinger-like Skyrme-Hartree-Fock equations. The role played by central, kinetic and spin-orbit contributions is discussed. We finally show that the effect of a tensor component in the effective interaction considerably favors the inversion of the two proton states in $^{48}$Ca.