{"record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"d27e537c6cfca7edc83bb1d1a3ac6a6f7c2032d379a625d4e8e7b61d80b86215","created":"2026-10-03T07:18:07Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["5475cf5dc5b1a72283d26dc95dc6e00d7ea4e00096a7c6492e409a1816eeb011"],"salt":"033d4b8988da01c61cd7e2be25b7a1bc46820b2575420b54ad7cc2f5795be17b","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"value","assisted_by":[],"external_id":"nuc.ab-initio-nuclei.lead-neutron-skin","kind":"well-posed","literature_status":"contested","n":"1","parents":[],"plain":"In heavy nuclei the extra neutrons form a thin outer skin whose thickness tells how the pressure of neutron-rich matter rises with density. Two Jefferson Lab experiments give values for lead and calcium that most nuclear models cannot fit at the same time.","posed_since":"2022","precise":"PREX-II gives $R_{\\mathrm{skin}}(208\\mathrm{Pb})$ = $R_{n} - R_{p}$ = 0.283 +/- 0.071 fm and CREX gives $R_{\\mathrm{skin}}(48\\mathrm{Ca})$ = 0.121 +/- 0.026 (exp) +/- 0.024 (model) fm. Determine whether a single nuclear Hamiltonian or energy density functional reproduces both measured parity-violating asymmetries $A_{\\mathrm{PV}}$, and fix $R_{\\mathrm{skin}}(208\\mathrm{Pb})$ to +/- 0.03 fm. Answer: a consistent description, or the identified experimental or theoretical cause of the tension.","problem_ref":null,"references":"","settled_by":"The MREX parity-violating experiment at the Mainz MESA accelerator, planned to reach roughly 0.03 fm on $R_{\\mathrm{skin}}(208\\mathrm{Pb})$, compared with ab initio predictions of both asymmetries.","status_note":"Ab initio calculations (Hu et al., Nature Physics 2022) predicted $R_{\\mathrm{skin}}(208\\mathrm{Pb})$ between 0.14 and 0.20 fm, compatible with PREX-II within about 1.5 standard deviations; the joint PREX-II and CREX tension for density functionals persisted as of 2026.","title":"Neutron skins of 208Pb and 48Ca from parity-violating scattering","topic_ref":"2e3c9bbdd2ce5849bb4ba420a815301d70db5fbf0341e1a0ed3d81994b4e4b35"},"attested":{"attestation":{"batch":null,"client_id":null,"id_token_sha256":null,"kind":"platform"},"record_hash":"6eeda053a8b70d3b04d4b6c2b0ac7ad8c196610fe332fee9e6dc87eb9bc58385","schema":"pubphys.attested/1"},"envelope":{"attested_hash":"ed618da74ae31a2b533605e5c5859aba3b8364765fe841bcad123e8e4d7ec2ea","platform_signature":{"key_id":"c6afc19b31429869751f06879c75cd64ea92654423d15b44be775bf1310a60da","sig":"iEHK2W0iSh1XFnler4a7FSOCEJMOd1AkdYXrcGiG0NcZ-BCZ2oheeaAjcPUL7hZIMuciqq-GwmRkEt7AuAVDCQ"},"schema":"pubphys.envelope/1"},"record_hash":"6eeda053a8b70d3b04d4b6c2b0ac7ad8c196610fe332fee9e6dc87eb9bc58385","leaf_index":1732}