Data-Driven Configuration-Interaction Hamiltonian Extrapolation to ⁶⁰Ca

Next generation experiments performed at newly built rare-isotope facilities will provide a greatly expanded view of the neutron rich calcium isotopes. In light of this, we aimed to produce a universal fp-shell interaction tailored to those isotopes which we call UFP-CA. Starting from a state-of-the-art IMSRG interaction, linear combinations of Hamiltonian parameters that define the natural basis of the parameter space are constrained by the latest experimental data for the very neutron-rich calcium, including the recently measured masses of ^55-57Ca [1]. We show that this data-driven method for improving the Hamiltonian provides an excellent description of the known binding energies and spectra for the calcium isotopes within the fp model space. This together with comparisons to results from energy-density functional  models leads us to conclude that ⁶⁰Ca is doubly-magic at a similar level to ⁶⁸Ni. Several predictions are presented for unobserved low-laying excited states in ^55-59Ca that should be accessible to future experiments.

[1] S. Michimasa et al., Phys. Rev. Lett. 121, 022506 (2018)