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

Abstract

New experimental data obtained from $\gamma$-ray tagged one-neutron and one-proton knockout from ${}^{55}$Co is presented. A candidate for the sought-after $T=1,T_z=0,J^{\pi }=6^{+}$ 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 $fp$-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-to-leading order (N${}^3$LO).

Comments: 6 pages, 5 figures. Work has been published