Role of the isovector spin-orbit potential in mitigating the CREX-PREX dilemma

Journal Article · Tue Jul 08 00:00:00 EDT 2025 · Physical Review. C

DOI:https://doi.org/10.1103/tcy2-brmk· OSTI ID:3018215

Kunjipurayil, Athul ^[1]; Piekarewicz, J. ^[1]; Salinas, Marc ^[2]

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1. Florida State University, Tallahassee, FL (United States)
2. Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)

Pioneering electroweak measurements of the neutron skin thickness in lead-208 and calcium-48 are challenging our understanding of nuclear dynamics. Many theoretical models suggest that the slope of the symmetry energy controls the development of a neutron skin in neutron-rich nuclei. This led to the expectation that if lead-208 exhibits a large neutron skin, calcium-48 should as well. Given that the PREX Collaboration reported a relatively thick neutron skin in lead, we anticipated that calcium would also have a significant neutron skin. Instead, the CREX Collaboration reported a thin neutron skin in calcium. Although many suggestions have been proposed, the “CREX-PREX dilemma” remains unsolved. Recently, an intriguing scenario has emerged, suggesting that an enhanced isovector spin-orbit interaction could simultaneously account for both results. Following this approach, we performed relativistic mean-field calculations with an increased isovector spin-orbit potential. Our findings indicate that, while this modification significantly affects the structure of calcium-48, it has only a marginal impact on lead-208, thereby bringing the results into better agreement with experiment. Furthermore, the strong enhancement required to mitigate the CREX-PREX dilemma destroys the agreement with a successful spin-orbit phenomenology, primarily by modifying the well-known ordering of spin-orbit partners.

• Research Organization: Florida State University, Tallahassee, FL (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Nuclear Physics (NP)
• Grant/Contract Number: FG02-92ER40750
• OSTI ID: 3018215
• Journal Information: Physical Review. C, Journal Name: Physical Review. C Journal Issue: 1 Vol. 112; ISSN 2469-9985; ISSN 2469-9993
• Publisher: American Physical Society (APS)
• Country of Publication: United States
• Language: English

Related Subjects

Neutron skin thickness
Nuclear astrophysics
Nuclear charge distribution
Nuclear density functional theory
Nuclear forces
Nuclear radii
Nucleon distribution