Electric dipole response of 208Pb from proton inelastic scattering: constraints on neutron skin thickness and symmetry energy

TL;DR

This study precisely measured the electric dipole response of 208Pb via proton scattering, providing constraints on neutron skin thickness and symmetry energy parameters relevant for nuclear structure and astrophysics.

Contribution

It offers new experimental data on E1 response of 208Pb and derives constraints on neutron skin thickness and symmetry energy, improving understanding of nuclear matter properties.

Findings

Neutron skin thickness of 208Pb is constrained to 0.168(+-0.009) fm.

Electric dipole polarizability is measured as 20.1+-0.6 fm^3.

A constraint band for symmetry energy parameters J and L is established.

Abstract

The electric dipole (E1) response of 208Pb has been precisely determined by measuring Coulomb excitation induced by proton scattering at very forward angles. The electric dipole polarizability, defined as inverse energy-weighted sum rule of the E1 strength, has been extracted as 20.1+-0.6 fm^3. The data can be used to constrain the neutron skin thickness of 208Pb to 0.168(+-0.009)_expt(+-0.013)_theo(+-0.021)_est fm, where the subscript "expt" refers to the experimental uncertainty, "theor" to the theoretical confidence band and "est" to the uncertainty associated with the estimation of the symmetry energy at the saturation density. In addition, a constraint band has been extracted in the plane of the symmetry energy (J) and its slope parameter (L) at the saturation density.