Impact of the nuclear symmetry energy on the pygmy dipole resonance

The correlation between the pygmy dipole strength and the symmetry energy of nuclear matter is reanalyzed. While previous calculations [A. Klimkiewicz et al., Phys. Rev. C 76, 051603(R) (2007); A. Carbone, G. Col\`o, A. Bracco, L.-G. Cao, P. F. Bortignon, F. Camera, and O. Wieland, Phys. Rev. C 81, 041301 (2010).] have clearly shown a direct correlation between both quantities, it remains unclear to what extent experimental as well as theoretical uncertainties can allow for an accurate determination of the symmetry energy. For this reason, we have recalculated the low-lying strength distributions of the giant dipole resonances for ¹³⁰Sn and ¹³²Sn that have been recently measured, taking into account the above uncertainties. The calculations are performed within two microscopic models, namely, the discrete quasiparticle random phase approximation (DRPA) and the quasiparticle continuum RPA, which is an extension of the DRPA that takes the coupling to the single-particle continuum into account in an exact way.