Implications of PREX-2 on the electric dipole polarizability of neutron-rich nuclei

Journal Article · 25 August 2021 · Physical Review C

DOI: https://doi.org/10.1103/PhysRevC.104.024329 · OSTI ID:1815016

Piekarewicz, Jorge  ^[1]

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1. Florida State Univ., Tallahassee, FL (United States); Florida State University

Background: The recent announcement by the PREX collaboration of an unanticipated thick neutron skin in ²⁰⁸Pb ($$R^{208}_{skin}$$) has challenged the understanding of neutron-rich matter in the vicinity of nuclear saturation density. Whereas earlier constraints indicate that the symmetry energy is relatively soft, the PREX-2 result seems to suggest the opposite. Purpose: To confront constraints on the symmetry energy obtained from measurements of the electric dipole polarizability against those informed by the PREX-2 measurement of $$R^{208}_{skin}$$ and by the correlations that it entails. Methods: Here, covariant energy density functionals informed by the properties of finite nuclei are used to compute the electric dipole response of ⁴⁸Ca, ⁶⁸Ni, ¹³²Sn, and ²⁰⁸Pb. The set of functionals used in this work are consistent with experimental data, yet are flexible enough in that they span a wide range of values of $$R^{208}_{skin}$$ Results: It is found that theoretical predictions of the electric dipole polarizability that are consistent with the PREX-2 measurement systematically overestimate the corresponding values extracted from the direct measurements of the distribution of electric dipole strength. Conclusions: The neutron skin thickness of ²⁰⁸Pb extracted from parity violating electron scattering and the electric dipole polarizability measured in photoabsorption experiments are two of the cleanest experimental tools used to constrain the symmetry energy around nuclear saturation density. However, the recent value of $$R^{208}_{skin}$$ that suggests a fairly stiff symmetry energy stands in stark contrast to the conclusions derived from the electric dipole polarizability. At present, I offer no solution to this dilemma.

• Research Organization: Florida State Univ., Tallahassee, FL (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Nuclear Physics (NP)
• Grant/Contract Number: FG02-92ER40750
• OSTI ID: 1815016
• Journal Information: Physical Review C, Journal Name: Physical Review C Vol. 104; ISSN 2469-9985
• Publisher: American Physical Society (APS)Copyright Statement
• Country of Publication: United States
• Language: English