{"record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"cd95ef215f3dc7a67b8474b6742796e3a9d51aa8b4b152004b2b854c0ea21a5b","created":"2026-10-03T07:17:53Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["5475cf5dc5b1a72283d26dc95dc6e00d7ea4e00096a7c6492e409a1816eeb011"],"salt":"d002a451155f88ca455557e0b62df9b136bc5f578d7a8b7d7220f7ffafd55287","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"identification","assisted_by":[],"external_id":"amo.bound-state-qed.proton-radius-residual","kind":"phenomenon","literature_status":"partially-resolved","n":"1","parents":[],"plain":"In 2010 muonic hydrogen (a muon orbiting a proton) gave a proton about 4% smaller than electron measurements did. New hydrogen measurements now agree with the small value, but some older hydrogen and scattering results still give the large value.","posed_since":"2010","precise":"Muonic hydrogen gives $r_p = 0.84087(39)\\,\\mathrm{fm}$ and the 2026 hydrogen 2S-6P measurement (Maisenbacher et al) gives $0.8406(15)\\,\\mathrm{fm}$, while the LKB 1S-3S (2018), H 2S-8D (2022) and Mainz electron scattering ($0.879\\,\\mathrm{fm}$) determinations favor larger values. Establish whether all hydrogen lines, combined with 1S-2S, yield a single (R_inf, r_p) pair consistent at the 1e-12 level in R_inf.","problem_ref":null,"references":"","settled_by":"A global fit of all hydrogen and deuterium transition frequencies, with outliers explained by identified systematics, giving R_inf and $r_p$ consistent with muonic values within uncertainties.","status_note":"The 2026 $2\\mathrm{S}-6\\mathrm{P}$ measurement agrees with muonic hydrogen and tests bound-state QED at 0.5 ppm; CODATA 2022 still reports a $2.8\\sigma$ difference between hydrogen-only and muonic data.","title":"Residual tensions in proton radius and Rydberg constant determinations","topic_ref":"49408e9491357ca694b4e9c3017e230cf2b78342f17900bd6e9221b8961376f4"},"attested":{"attestation":{"batch":null,"client_id":null,"id_token_sha256":null,"kind":"platform"},"record_hash":"c8fb1852ecb4a0cd3bd5349236cf4d3c9cecb666980f4c0ebefc81995860a8f7","schema":"pubphys.attested/1"},"envelope":{"attested_hash":"e4a28d60da6f5887d92fbc5f64e64d0cd5ac88549f558b90314d5ec5a7598659","platform_signature":{"key_id":"c6afc19b31429869751f06879c75cd64ea92654423d15b44be775bf1310a60da","sig":"oRasl6L3gSku-ZZ-OLa-pgj3TqK-BK59EqKm6VjfMZFlx5vqaKXeBkxVpGCM50yJaGOzisX9thgzVkP-rbXYCA"},"schema":"pubphys.envelope/1"},"record_hash":"c8fb1852ecb4a0cd3bd5349236cf4d3c9cecb666980f4c0ebefc81995860a8f7","leaf_index":376}