Connecting the Pygmy Dipole Resonance to the neutron skin

TL;DR

This paper investigates the link between neutron skin thickness and the pygmy dipole resonance (PDR) using microscopic models, finding a linear correlation that can help constrain nuclear symmetry energy properties.

Contribution

It introduces a microscopic transport model analysis connecting PDR properties to neutron skin and symmetry energy, providing a method to estimate neutron skin from PDR measurements.

Findings

PDR energy centroid follows E_{PDR}=41 A^{-1/3}

Linear correlation between PDR EWSR and neutron skin thickness

A 15 MeVfm^2 increase in EWSR corresponds to 0.1fm neutron skin increase

Abstract

We study the correlation between the neutron skin development and the low-energy dipole response associated with the pygmy dipole resonance (PDR) in connection with the properties of symmetry energy. We perform our investigation within a microscopic transport model based on the Landau-Vlasov kinetic equation by employing three different equations of state in the isovector sector. Together with the giant dipole resonance (GDR) for all studied systems, we identify a PDR collective mode whose energy centroid is very well described by the parametrization E_{PDR}=41 A^{-1/3}. A linear correlation between the energy weighted sum rule (EWSR) associated to PDR and the neutron skin thickness is evidenced. An increase of 15 MeVfm^2 of EWSR, in correspondence to a change of 0.1fm of the neutron skin size, is obtained. We conjecture that different nuclei having close neutron skin sizes will exhaust the same EWSR in the pygmy region. This suggests that a precise experimental estimate of the total EWSR exhausted by the PDR allows the determination of the neutron skin size, constraining the slope parameter of the symmetry energy.