Abstract
The density dependence of the symmetry energy around saturation density, characterized by the slope parameter L , is studied using information provided by the neutron skin thickness in finite nuclei. An estimate for L is obtained from experimental data on neutron skins extracted from antiprotonic atoms. We also discuss the ability of parity-violating elastic electron scattering to obtain information on the neutron skin thickness in 208Pb and to constrain the density dependence of the nuclear symmetry energy. The size and shape of the neutron density distribution of 208Pb predicted by mean-field models is briefly addressed. We conclude with a comparative overview of the L values predicted by several existing determinations.
Highlights
The nuclear symmetry energy is a fundamental quantity in nuclear physics and astrophysics because it governs important properties of very small entities like atomic nuclei (R ∼ 10−15 m) and of very large objects like neutron stars (R ∼ 104 m) [1]
It implies a central value for Δrnp that lies both within the range between 0.15 and 0.22 fm suggested by the experiments with strong probes [33, 84], and within the range between 0.14 and 0.20 fm suggested by recent constraints on the nuclear Equation of State (EOS) derived from observed masses and radii of neutron stars [85, 86]
The results from microscopic Brueckner-Hartree-Fock calculations including effective three-body forces give L = 66.5 MeV [93]. These values for the slope of the symmetry energy are consistent with the range around L ∼ 40– 60 MeV predicted by an empirical EOS constrained exclusively on the basis of astrophysical observations [85]
Summary
The nuclear symmetry energy is a fundamental quantity in nuclear physics and astrophysics because it governs important properties of very small entities like atomic nuclei (R ∼ 10−15 m) and of very large objects like neutron stars (R ∼ 104 m) [1]. Experimental informations from nuclear masses, heavyion reactions, giant resonances, and observational properties of neutron stars, constrain J in a range between 30 and 35 MeV [28,29]. These values are, in general, predicted by successful nuclear mean-field models. We will study the constraints that can be derived from the analysis of neutron skins in antiprotonic atoms, and the constraints that may be provided by parity-violating elastic electron scattering in a heavy neutron-rich nucleus such as 208Pb. We discuss the size and shape of the neutron density distribution of 208Pb predicted by mean-field models and its dependence with the symmetry energy. A summary and outlook are given to conclude the paper
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