Data-driven configuration-interaction Hamiltonian extrapolation to <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mmultiscripts><mml:mi>Ca</mml:mi><mml:mprescripts/><mml:none/><mml:mn>60</mml:mn></mml:mmultiscripts></mml:math>
A. Magilligan, B. A. Brown, S. R. Stroberg
Abstract
Following the many successful implementations of effective universal configuration-interaction Hamiltonians, we endeavored to produce a universal $fp$ shell interaction tailored for the calcium isotopes, which we call UFP-CA. Starting from a state-of-the-art in-medium similarity renormalization group (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 neutron-rich calcium isotopes. 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 $^{60}\mathrm{Ca}$ is doubly magic at a similar level to $^{68}\mathrm{Ni}$. Several predictions are presented for unobserved low-lying excited states in $^{55\ensuremath{-}59}\mathrm{Ca}$ that will be accessible to future experiments.