Isospin-Based Supersymmetry in Neutron-Proton Pairing gap of fp-Shell Nuclei

Abstract

This study presents a systematic investigation of the effects of isospin, including both T=0 and T=/0 components, on nucleon pairing correlations in fp-shell nuclei. To this aim, the interacting boson model-4, which explicitly incorporates isospin and spin degrees of freedom, is employed to examine various mass formulas associated with neutron-proton correlations in atomic nuclei. Within this framework, neutron-proton pairing gaps are derived for the first time, providing a unified description of pairing correlations in even-even, odd-A, and odd-odd systems. Furthermore, to achieve a more realistic representation of local nuclear dynamics, effective asymmetric weighting coefficients are introduced into the conventional pairing-gap expressions, motivated by physical considerations related to shell structure, blocking effects, and isospin symmetry. These coefficients are determined through a fit to experimental binding-energy data and lead to a significant improvement in the agreement between theoretical predictions and observed systematic. Additionally, the results support the central assumption regarding the supersymmetry of the first fp-shell nuclei, highlighting the essential role of isospin-dependent effects in shaping neutron-proton pairing collectivity.