Quasiparticle random-phase approximation with quasiparticle-vibration coupling : Application to the Gamow-Teller response of the superfluid nucleus Sn 120

We propose a self-consistent quasiparticle random-phase approximation (QRPA) plus quasiparticle-vibration coupling (QPVC) model with Skyrme interactions to describe the width and the line shape of giant resonances in open-shell nuclei, in which the effect of superfluidity should be taken into account in both the ground state and the excited states. We apply the new model to the Gamow-Teller resonance in the superfluid nucleus Sn120, including both the isoscalar spin-triplet and the isovector spin-singlet pairing interactions. The strength distribution in Sn120 is well reproduced and the underlying microscopic mechanisms, related to QPVC and also to isoscalar pairing, are analyzed in detail.