Isoscalar neutron-proton pairing and SU(4)-symmetry breaking in Gamow-Teller transitions

TL;DR

This paper investigates the role of isoscalar neutron-proton pairing in Gamow-Teller transitions within shell-model calculations, revealing its significant influence on transition strength distribution and symmetry breaking in nuclei around A=42.

Contribution

It provides a detailed analysis of isoscalar pairing effects and SU(4) symmetry breaking in Gamow-Teller transitions using large-scale shell-model calculations with realistic interactions.

Findings

Isoscalar T=0, J=1+ pairing influences GT strength concentration.

Suppression of GT strengths in certain nuclei is due to spin-orbit and quadrupole interactions.

Isoscalar pairing condensation probability is less than 60% near SU(4) symmetry.

Abstract

The isoscalar neutron-proton pairing is thought to be important for nuclei with equal number of protons and neutrons but its manifestation in structure properties remains to be understood. We investigate the Gamow-Teller (GT) transitions for the f7/2-shell nuclei in large-scale shell-model calculations with the realistic Hamiltonian. We show that the isoscalar T=0, J=1+ neutron-proton pairing interaction plays a decisive role for the concentration of GT strengths at the first-excited 1+ state in 42Sc, and that the suppression of these strengths in 46V, 50Mn, and 54Co is mainly caused by the spin-orbit force supplemented by the quadrupole-quadrupole interaction. Based on the good reproduction of the charge-exchange reaction data, we further analyze the interplay between the isoscalar and isovector pairing correlations. We conclude that even for the most promising A=42 nuclei where the SU(4) isoscalar-isovector-pairing symmetry is less broken, the probability of forming an isoscalar neutron-proton pairing condensation is less than 60% as compared to the expectation at the SU(4)-symmetry limit.