An alternative understanding of mass formulas in terms of nuclear structure

A typical form of mass formula is re-explained in terms of nuclear structure. For $ N \approx Z $ nuclei, we propose to start with the shell model picture and to consider the T=0 $2n-2p$ ($\alpha$-like) correlations as the fundamental concept, instead of the symmetry energy. Subsequently, the symmetry energy is described on the basis of the $\alpha$-like superfluidity caused by the T=0 $2n-2p$ correlations, in parallel with the pairing energy described on the basis of the pairing superfluidity. This re-explanation gives useful insight for understanding the nuclear mass formula. The origin of the Wigner energy is also explained in an interacting boson model for the Cooper pairs in the $\alpha$-like superfluid vacuum. Adding a correction term due to the T=0 $2n-2p$ correlations, which determines the T=0 base level for nuclear masses, can improve the mass formulas in practice.