Isoscalar 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.

This study aims to investigate the effects of the isoscalar pairing interaction on GT and spin-dipole (SD) transitions in ⁴²Ca.

By 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.

For 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.

Isoscalar 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.