Effects of core excitations in the violation of the nuclear particle-particle to particle-hole transformation

A core excited shell model for the mass-40 region is developed to account for the discrepancies between particle-particle (pp) and particle-hole (ph) nuclear partners. Explicitly, second order perturbative-type calculations are incomplete when used in an attempt to simultaneously account for the spectral discrepancies between ⁴⁰K(vf _{7 2}^-πd _{3 2}^-) and the Racah transform of ³⁸Cl(vf _{7 2}^-πd _{3 2}) and those between ⁴⁸Sc(πf _{7 2}^-vf _{7 2}^-1) and the Racah transform of ⁴²Sc(πf _{7 2}^-vf _{7 2}). However, an (fd) shell model, which includes core excitations (multi-particle, multi-hole states) from the 0d _{3 2} shell to the 0f _{7 2} shell, yields the cancellation of the second order perturbative-type results which is necessary for a satisfactory explanation for both sets of spectral discrepancies. The usefulness of the model in the investigation of the positioning of core excited states in ⁴⁰Ca (like 8p-8h) and in the generation of effective operators is also explored.