Effects of isoscalar pairing force on spin-isospin transitions in 42Ca

Abstract

BackgroundIsoscalar pairing plays an important role in the spin-isospin excitation of nuclei. The discovery of super Gamow-Teller (GT) states in N≈Z nuclei has motivated researchers to explore the effects of isoscalar pairing on spin-isospin excitations.PurposeThis study aims to investigate the effects of the isoscalar pairing interaction on GT and spin-dipole (SD) transitions in 42Ca.MethodsBy solving the relativistic Hartree-Bogoliubov equation, we obtained the canonical single-nucleon basis and occupation amplitudes, which were used as inputs for the quasiparticle phase-random approximation (QRPA) calculation. Using the QRPA model, the GT and SD transitions in 42Ca were calculated, where the Gaussian isoscalar pairing force was adopted, with its strength being a free parameter.ResultsFor GT states, the isoscalar pairing mixed the spin-flip transition configuration into the low-lying GT state, enhancing the collectivity of the low-energy GT state and significantly increasing its transition strength. Meanwhile, the isoscalar pairing force induced a shift of the low-energy GT state toward lower energies owing to the attractive properties of the isoscalar pairing force. For SD states, the isoscalar pairing force hardly affected the strengths and energies of SD states in 42Ca.ConclusionsIsoscalar pairing force was essential for restoring the SU(4) symmetry and hence reproducing the low-energy super GT state of 42Ca in the experiment, whereas it hardly affected the SD states.

Keywords

• covariant density-functional theory
• qrpa model
• isoscalar pairing force
• spin-isospin excitation