{"paper":{"title":"On the nature of $a_1(1420)$","license":"http://arxiv.org/licenses/nonexclusive-distrib/1.0/","headline":"","cross_cats":[],"primary_cat":"hep-ph","authors_text":"Andrey Sarantsev, Bernhard Ketzer, Mikhail Mikhasenko","submitted_at":"2015-01-28T08:18:22Z","abstract_excerpt":"The resonance-like signal with axial-vector quantum numbers $J^{PC}=1^{++}$ at a mass of $1420\\,$MeV and a width of $140\\,$MeV, recently observed by the COMPASS and VES experiments in the $f_0(980)\\pi$ final state and tentatively called $a_1(1420)$, is discussed. Instead of a genuine new meson, we interpret this signal as a dynamical effect due to a singularity (branching point) in the triangle diagram formed by the processes $a_1(1260) \\to K^\\star \\bar{K}$, $K^\\star\\to K\\pi$, and $K \\bar{K} \\to f_0(980)$ (+ c.c). The amplitude for this diagram is calculated. The result exhibits a peak in the "},"claims":{"count":0,"items":[],"snapshot_sha256":"258153158e38e3291e3d48162225fcdb2d5a3ed65a07baac614ab91432fd4f57"},"source":{"id":"1501.07023","kind":"arxiv","version":2},"verdict":{"id":null,"model_set":{},"created_at":null,"strongest_claim":"","one_line_summary":"","pipeline_version":null,"weakest_assumption":"","pith_extraction_headline":""},"references":{"count":0,"sample":[],"resolved_work":0,"snapshot_sha256":"258153158e38e3291e3d48162225fcdb2d5a3ed65a07baac614ab91432fd4f57","internal_anchors":0},"formal_canon":{"evidence_count":0,"snapshot_sha256":"258153158e38e3291e3d48162225fcdb2d5a3ed65a07baac614ab91432fd4f57"},"author_claims":{"count":0,"strong_count":0,"snapshot_sha256":"258153158e38e3291e3d48162225fcdb2d5a3ed65a07baac614ab91432fd4f57"},"builder_version":"pith-number-builder-2026-05-17-v1"}