On the masses of A = 54 isospin septet and the isobaric multiplet mass equation * *Supported in part by the National Key R&D Program of China (2018YFA0404401, 2016YFA0400504), National Natural Science Foundation of China (11975280, 11905259)

Abstract

Using the ground-state mass of 52Ni and two-proton decay energy of 54Zn, the ground-state mass excess of 54Zn is deduced to be –6504(85) keV. This value is about 2 MeV lower than the prediction of the quadratic form of the isobaric multiplet mass equation (IMME). A cubic fit to the existing mass data of the , isospin multiplet yields a surprisingly large d coefficient of IMME, i.e., , being deviated from zero, and the resultant ratio significantly deviates from the systematics. This phenomenon is analyzed in this study, and we conclude that the breakdown of the quadratic form of IMME could be likely due to the mis-assignment of the isobaric analog state (IAS) in the nucleus 54Fe or extremely strong isospin mixing.