Article révisé par les pairs
| Résumé : | We construct two new Hartree-Fock-Bogoliubov mass models, labeled HFB-28, HFB-29, which in addition to the generalized Skyrme form containing t4 and t5 terms, also include now a modified spin-orbit force. This alternative spin-orbit force allows for an unconventional isospin and/or density dependence relative to the traditional form included in Skyrme functionals. The new forces underlying these models are fitted to essentially all mass data and at the same time to a realistic equation of state of neutron matter. The inclusion of the modified spin-orbit terms allows us to reduce the rms deviation with respect to all the 2353 known masses with Z, N≥8 by 20 keV, leading to a final model error of 0.52 MeV. It is shown that the newly optimized spin-orbit forces do not conform with the one deduced from the relativistic mean field theory, and consequently that the relativistic spin-orbit force might not be optimum to reproduce experimental masses. The spin-orbit splittings are shown to be reduced and in better agreement with empirical values when including a density-dependent form of the spin-orbit interaction. However, the new mass models with such modified spin-orbit terms still fail to reproduce the kink seen in the isotopic shift of the K or Pb charge radii around the neutron magic numbers, despite the fact that such generalizations of the spin-orbit terms were also introduced to improve the description of the isotopic shifts. Shell effects, in particular far away from stability, are shown to remain unaffected by the new spin-orbit terms, except at the N=184 magic number. |
