Experimental identification of the $T = 1$, $J^π = 6^+$ state of $^{54}$Co and isospin symmetry in $A = 54$ studied via one-nucleon knockout reactions

Abstract

New experimental data obtained from γ-ray tagged one-neutron and one-proton knockout from 55 Co is presented. A candidate for the sought-after T = 1, Tz = 0, J π = 6 + state in 54 Co is proposed based on a comparison to the new data on 54 Fe, the corresponding observables predicted by large-scale-shell-model (LSSM) calculations in the full f p-model space employing charge-dependent contributions, and isospin-symmetry arguments. Furthermore, possible isospin-symmetry breaking in the A = 54, T = 1 triplet is studied by calculating the experimental c coefficients of the isobaric mass multiplet equation (IMME) up to the maximum possible spin J = 6 expected for the (1f 7/2 ) −2 two-hole configuration relative to the doubly-magic nucleus 56 Ni. The experimental quantities are compared to the theoretically predicted c coefficients from LSSM calculations using two-body matrix elements obtained from a realistic chiral effective field theory potential at next-to-next-to-next-toleading order (N 3 LO).