{"paper":{"title":"Observation of a $B_c^{*+}$ meson with the ATLAS detector","license":"http://creativecommons.org/licenses/by/4.0/","headline":"ATLAS observes the B_c^{*+} meson decaying to B_c^+ plus a photon with over 8 sigma significance","cross_cats":[],"primary_cat":"hep-ex","authors_text":"ATLAS Collaboration","submitted_at":"2026-05-15T17:39:38Z","abstract_excerpt":"The first observation of a new meson state decaying into $B_c^+$ and a photon is presented using a dataset of $pp$ collisions at a centre-of-mass energy $\\sqrt{s} = 13$ TeV collected by the ATLAS detector at the Large Hadron Collider, corresponding to an integrated luminosity of 140 fb$^{-1}$. The $B_c^+$ mesons are reconstructed from a three-muon final state from $B_c^+\\to J/\\psi(\\mu^+\\mu^-)\\mu^+\\nu_\\mu X$ decays, along with photons reconstructed via conversions to electron-positron pairs in the detector material. The new state is observed with a significance that exceeds 8 standard deviation"},"claims":{"count":4,"items":[{"kind":"strongest_claim","text":"The new state is observed with a significance that exceeds 8 standard deviations. The mass difference between the new meson state and the ground-state B_c^+ meson is measured to be 64.5 ± 1.4(stat.)^{+1.0}_{-1.4}(syst.) MeV. This corresponds to a mass for the observed state of 6339.0 ± 1.4(stat.)^{+1.0}_{-1.4}(syst.) ± 0.3(m_{B_c^+}) MeV. The low mass difference value matches the theory expectations for the lowest vector state of the b-bar c quarkonium system, the B_c^{*+} meson.","source":"verdict.strongest_claim","status":"machine_extracted","claim_id":"C1","attestation":"unclaimed"},{"kind":"weakest_assumption","text":"The photons reconstructed via conversions to electron-positron pairs in the detector material, together with the three-muon final state, correctly isolate the signal without significant contamination from misidentified backgrounds or other processes that could produce a fake peak at the reported mass difference.","source":"verdict.weakest_assumption","status":"machine_extracted","claim_id":"C2","attestation":"unclaimed"},{"kind":"one_line_summary","text":"First observation of the B_c^{*+} meson with mass difference 64.5 MeV from the ground-state B_c^+ at >8 sigma significance using ATLAS data.","source":"verdict.one_line_summary","status":"machine_extracted","claim_id":"C3","attestation":"unclaimed"},{"kind":"headline","text":"ATLAS observes the B_c^{*+} meson decaying to B_c^+ plus a photon with over 8 sigma significance","source":"verdict.pith_extraction.headline","status":"machine_extracted","claim_id":"C4","attestation":"unclaimed"}],"snapshot_sha256":"ac72232901f23d025baf28ca9be68b73a9eee976c550e0f7531e8e9d2bdf9bf9"},"source":{"id":"2605.16228","kind":"arxiv","version":1},"verdict":{"id":"157e78da-9298-4271-85e1-58f0b61ce02e","model_set":{"reader":"grok-4.3"},"created_at":"2026-05-19T18:14:51.096680Z","strongest_claim":"The new state is observed with a significance that exceeds 8 standard deviations. The mass difference between the new meson state and the ground-state B_c^+ meson is measured to be 64.5 ± 1.4(stat.)^{+1.0}_{-1.4}(syst.) MeV. This corresponds to a mass for the observed state of 6339.0 ± 1.4(stat.)^{+1.0}_{-1.4}(syst.) ± 0.3(m_{B_c^+}) MeV. The low mass difference value matches the theory expectations for the lowest vector state of the b-bar c quarkonium system, the B_c^{*+} meson.","one_line_summary":"First observation of the B_c^{*+} meson with mass difference 64.5 MeV from the ground-state B_c^+ at >8 sigma significance using ATLAS data.","pipeline_version":"pith-pipeline@v0.9.0","weakest_assumption":"The photons reconstructed via conversions to electron-positron pairs in the detector material, together with the three-muon final state, correctly isolate the signal without significant contamination from misidentified backgrounds or other processes that could produce a fake peak at the reported mass difference.","pith_extraction_headline":"ATLAS observes the B_c^{*+} meson decaying to B_c^+ plus a photon with over 8 sigma significance"},"integrity":{"clean":true,"summary":{"advisory":0,"critical":0,"by_detector":{},"informational":0},"endpoint":"/pith/2605.16228/integrity.json","findings":[],"available":true,"detectors_run":[{"name":"doi_title_agreement","ran_at":"2026-05-19T18:31:18.720531Z","status":"completed","version":"1.0.0","findings_count":0},{"name":"doi_compliance","ran_at":"2026-05-19T18:21:10.481496Z","status":"completed","version":"1.0.0","findings_count":0},{"name":"shingle_duplication","ran_at":"2026-05-19T17:49:42.205544Z","status":"skipped","version":"0.1.0","findings_count":0},{"name":"citation_quote_validity","ran_at":"2026-05-19T17:49:41.823429Z","status":"skipped","version":"0.1.0","findings_count":0},{"name":"ai_meta_artifact","ran_at":"2026-05-19T17:33:23.133365Z","status":"skipped","version":"1.0.0","findings_count":0},{"name":"external_links","ran_at":"2026-05-19T17:31:28.443525Z","status":"completed","version":"1.0.0","findings_count":0},{"name":"cited_work_retraction","ran_at":"2026-05-19T16:51:58.532973Z","status":"completed","version":"1.0.0","findings_count":0},{"name":"claim_evidence","ran_at":"2026-05-19T16:41:55.372374Z","status":"completed","version":"1.0.0","findings_count":0}],"snapshot_sha256":"b1688d5e06bcf28abe32ba192603b25c878fe5e3dd8d9ad9a92cd8bcbe411f75"},"references":{"count":66,"sample":[{"doi":"","year":2004,"title":"Brambilla et al.,Heavy Quarkonium Physics, 2004, arXiv:hep-ph/0412158","work_id":"cd454890-d3ff-4cfe-9608-6947da711f74","ref_index":1,"cited_arxiv_id":"","is_internal_anchor":false},{"doi":"","year":1992,"title":"Y.-Q. Chen and Y.-P. Kuang, Improved QCD-motivated heavy-quark potentials with explicitΛM𝑆 dependence, Phys. Rev. D46(1992) 1165","work_id":"c4ed06a8-ff51-40d9-b3a4-44fe52518caa","ref_index":2,"cited_arxiv_id":"","is_internal_anchor":false},{"doi":"","year":1993,"title":"L. P. Fulcher, Z. Chen and K. C. Yeong, Energies of quark-antiquark systems, the Cornell potential, and the spinless Salpeter equation, Phys. Rev. D47(1993) 4122","work_id":"87e582e3-ff51-4c90-9a89-2d54668ad9ca","ref_index":3,"cited_arxiv_id":"","is_internal_anchor":false},{"doi":"","year":2019,"title":"The excited bottom-charmed mesons in a nonrelativistic quark model","work_id":"c7cb61f2-157f-4472-bc77-e595e44db16d","ref_index":4,"cited_arxiv_id":"1903.11927","is_internal_anchor":true},{"doi":"","year":2022,"title":"G.-L. Wang, T. Wang, Q. Li and C.-H. Chang, The mass spectrum and wave functions of the B𝑐 system, JHEP05(2022) 006, arXiv:2201.02318 [hep-ph]","work_id":"ca886c07-8945-4ec4-b01c-7dc5fda454fb","ref_index":5,"cited_arxiv_id":"","is_internal_anchor":false}],"resolved_work":66,"snapshot_sha256":"24c8133d775a2f75ef39d398d4c62a71b7ace20101416a6d333e25bba730e13f","internal_anchors":41},"formal_canon":{"evidence_count":1,"snapshot_sha256":"691e2437a46b56d4245039b4ff968834c9ee661fdfbea636999e98ac8f8ba0f6"},"author_claims":{"count":0,"strong_count":0,"snapshot_sha256":"258153158e38e3291e3d48162225fcdb2d5a3ed65a07baac614ab91432fd4f57"},"builder_version":"pith-number-builder-2026-05-17-v1"}