{"record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"fa2f7f6ee880f4f6332f7c64c475f85b9bbb8b855418fdb237c44bc7e5743ebd","created":"2026-10-03T07:17:54Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["5475cf5dc5b1a72283d26dc95dc6e00d7ea4e00096a7c6492e409a1816eeb011"],"salt":"c63c7561cbf8ec4d2db90c7c5ac93064cdd9a4476dba85c2490fc552f454e26c","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"value","assisted_by":[],"external_id":"amo.muonic-atoms.muonium-spectroscopy","kind":"well-posed","literature_status":"open","n":"1","parents":[],"plain":"Muonium, an antimuon holding an electron, contains no proton, so its energy levels test the theory of light and charges without nuclear-structure uncertainty and give the muon mass and magnetism. Its best measurements date from about 25 years ago.","posed_since":"","precise":"The muonium ground-state hyperfine interval (about $4.463\\,\\mathrm{GHz}$) was last measured at LAMPF in 1999 and the $1\\mathrm{S}-2\\mathrm{S}$ two-photon interval at RAL in 2000. Improve both by at least a factor of 10 (MuSEUM at J-PARC for the hyperfine interval, Mu-MASS at PSI for $1\\mathrm{S}-2\\mathrm{S}$) and determine $m_\\mu/m_e$ and $\\mu_\\mu/\\mu_p$ from them, testing whether the two routes and QED theory agree.","problem_ref":null,"references":"","settled_by":"New muonium hyperfine and 1S-2S measurements, each with an uncertainty at least ten times below the 1999-2000 values, combined with bound-state QED theory to yield consistent $m_{\\mu}/m_e$ values.","status_note":"MuSEUM reported ongoing hyperfine measurements at J-PARC aiming at a tenfold improvement in 2025 (arXiv 2501.02736).","title":"Muonium hyperfine and 1S-2S intervals at improved precision","topic_ref":"2380a3f4f6cf855245dd94f150e2cf50d6152e19302311f341aa833f6dfe7a59"},"attested":{"attestation":{"batch":null,"client_id":null,"id_token_sha256":null,"kind":"platform"},"record_hash":"d8a9ec10e0c8ce1f600a32f6b5e30123082ea38c1e0e558311ba655e08b94674","schema":"pubphys.attested/1"},"envelope":{"attested_hash":"0f8496fdbf9054a3a61079fc5b242be82410f1c02e70e224fe634d4213acc651","platform_signature":{"key_id":"c6afc19b31429869751f06879c75cd64ea92654423d15b44be775bf1310a60da","sig":"jGoXxLjyvkfP-Y16xdEcxuCaMPsNE3wyCjeRBAEHg0bxY9HE1ZGEos69TW4_Fi2t6Jro6KiOzxLaqnGHulN0Ag"},"schema":"pubphys.envelope/1"},"record_hash":"d8a9ec10e0c8ce1f600a32f6b5e30123082ea38c1e0e558311ba655e08b94674","leaf_index":429}