Low-lying dipole response: Isospin character and collectivity in68Ni,132Sn, and208Pb

Experimental results on the Pygmy Dipole Resonance

“…While the lower lying J π = 1 − states have transition densities showing the signature of a neutron skin oscillation, this signature is vanishing in the higher lying states, which causes the reduction of the IS E1 strength [27]. A similar reduction of the IS E1 strength compared to the EM response is also observed in other calculations [7,30]. The combination of experiments using complementary probes with different sensitivity to the radial dependence of the transition densities and modern microscopic calculations thus might provide for the first time an identification of the neutron skin signature of the low-lying E1 strength.…”

Neutron skin thickness from the measured electric dipole polarizability inNi68,Sn120, andRoca-Maza1, Viñas2, Centelles3 et al. 2015Phys. Rev. CSelf Cite226322563View full textAdd to dashboardCite

“…This choice allows one to estimate the neutron skin thickness of 68 Ni, 120 Sn, and 208 Pb using the fits displayed in Eq. (9). The resulting values for ∆r np in 68 Ni, 120 Sn and 208 Pb are given in the last column of Table I.…”

“…In addition to the identification of the prominent Giant Dipole Resonance (GDR), the electric dipole response of neutron-rich nuclei displays a smaller concentration of strength at lower energies, that is commonly referred to as the Pygmy Dipole Strength (PDS) [5]. Data on the PDS have been used in the past to constrain the symmetry energy and to obtain * xavier.roca.maza@mi.infn.it information on the neutron skin thickness of neutronrich nuclei [6][7][8][9][10][11]. In one of the earliest applications of uncertainty quantification to the domain of energy density functionals (EDFs), Reinhard and Nazarewicz carried out a covariance analysis to correlate the neutron skin thickness of 208 Pb to the properties of both finite nuclei and infinite nuclear matter [1].…”

Microscopic calculations beyond mean-field with zero-range effective interactions

“…The isoscalar dipole state is subtracted using the procedure explained in the Appendix A of Ref. [21]. A lower cutoff on the collectivity of the intermediate phonon states is needed for at least two reasons: firstly, RPA is known to be not reliable for non-collective states, and secondly, introducing poorly collective phonons would oblige to account for the issue of the Pauli principle correction.…”