Nuclear giant resonances studied with quasiparticle-vibration coupling model and populated by vortex γ-photons

Investigating giant resonances is essential for deepening our understanding of nuclear structure and constraining the nuclear matter equation of state. In this work, we explore both giant dipole and quadrupole resonances in the superfluid nucleus 112Sn based on a fully self-consistent quasiparticle-vibration coupling (QPVC) theory with the Skyrme interaction. Incorporating QPVC effects refines the description of the isoscalar and isovector modes by producing a downward energy shift and a broader width that are more consistent with experimental observations. Based on quasiparticle random phase approximation (QRPA) and QPVC model, the photoabsorption cross sections are further studied. It is shown that plane-wave γ-photons predominantly excite the electric dipole (E1) mode. In contrast, when the nucleus aligns with the beam, vortex γ-photons selectively excite the transition with a certain multipolarity through new selection rules given by angular momentum conservation. When the nucleus is offset from the beam axis, angular momentum selection rules relax, allowing the E1 component to gradually recover and supplant the electric quadrupole or octupole transitions, while the oscillatory behavior of the Bessel functions governs fluctuations in the E1 cross section. By comparing QRPA and QPVC results, QPVC shows its effect in the high energy range of vortex photon absorption cross sections at small impact parameters.