Effects of the tensor force on the ground state and first 2+ states of the magic Ca 54 nucleus

Abstract

The magic nature of the Ca54 nucleus is investigated in light of recent experimental results. We employ both Hartree-Fock-Bogoliubov and Hartree-Fock (HF)+BCS methods using Skyrme-type SLy5, SLy5+T, and T44 interactions. The evolution of the single-particle spectra is studied for the N=34 isotones: Fe60, Cr58, Ti56, and Ca54. An increase is obtained in the neutron spin-orbit splittings of p and f states due to the effect of the tensor force which also makes Ca54 a magic nucleus candidate. Quasiparticle random-phase approximation calculations on top of HF+BCS are performed to investigate the first Jπ=2+ states of the calcium isotopic chain. A good agreement for excitation energies is obtained when we include the tensor force in the mean-field part of the calculations. The first 2+ states indicate a subshell closure for both Ca52 and Ca54 nuclei. We confirm that the tensor part of the interaction is quite essential in explaining the neutron subshell closure in Ca52 and Ca54 nuclei. © 2014 American Physical Society.