{
  "abstract": "A bstract : An enhancement in the three-pion energy at around $$ \\sqrt{s} $$ s ≈ 1.42 GeV with a ₁ quantum numbers was observed at the COMPASS experiment. This was later attributed to the triangle singularity mechanism involving an on-shell K ∗ (892), K and $$ \\overline{K} $$ K ¯ intermediate states. The alignment of the decay K with the spectator $$ \\overline{K} $$ K ¯ produces an f ₀ (980), resulting in a kinematic enhancement, which is classically explained by the Landau equations. However, this one-loop process forms only part of a non-diagonal transition in a much larger coupled-channel framework. This study demonstrates the feasibility of embedding one-loop triangle-singularity calculations into a unitary three-body amplitude allowing one to consistently incorporate final-state interactions and their potentially substantial effect. For this, up to P -wave isobars and all sub-channel isospins are combined in a nine-channel production amplitude that is fitted to COMPASS lineshapes at different momentum transfers. The fitted amplitude reproduces the narrow enhancement in the ( πf ₀ ) P channel near $$ \\sqrt{s} $$ s ≈ 1 . 42 GeV. This implies that the triangle singularity mechanism sufficiently explains the observed enhancement, and an additional genuine a ₁ (1420) pole is not required. Incidentally, the parameters of the ground state axial vector resonance (the a ₁ (1260)) are also extracted from that data.",
  "abstract_shown": true,
  "affiliations": [
    "Universität Bonn",
    "The George Washington University",
    "Theory Center, Thomas Jefferson National Accelerator Facility",
    "University of Bern"
  ],
  "article_type": null,
  "arxiv": null,
  "author_total": 4,
  "authors": [
    {
      "affs": [
        0
      ],
      "name": "Ajay S. Sakthivasan",
      "orcid": "0009-0002-9306-5956"
    },
    {
      "affs": [
        1
      ],
      "name": "Yuchuan Feng",
      "orcid": "0009-0001-1095-6829"
    },
    {
      "affs": [
        1,
        2
      ],
      "name": "Michael Döring",
      "orcid": "0000-0002-2676-5517"
    },
    {
      "affs": [
        1,
        3
      ],
      "name": "Maxim Mai",
      "orcid": "0000-0003-0119-0718"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/74s167mt67qm1.bib",
  "cited_by": 0,
  "doi": "10.1007/jhep10(2026)045",
  "fulltext_url": null,
  "id": "74s167mt67qm1",
  "issns": [
    "1029-8479"
  ],
  "landing_url": "https://link.springer.com/10.1007/JHEP10(2026)045",
  "language": null,
  "licence": "CC-BY-4.0",
  "licence_label": "CC BY 4.0",
  "licence_source": "article",
  "licence_url": "https://creativecommons.org/licenses/by/4.0",
  "metadata_licence": null,
  "native_subjects": [
    [
      "openalex",
      "3106|Quantum Chromodynamics and Particle Interactions"
    ]
  ],
  "openalex": "W7165778270",
  "pdf_url": "https://link.springer.com/content/pdf/10.1007/JHEP10(2026)045.pdf",
  "pmcid": null,
  "pmid": null,
  "published": "2026-10-05",
  "publisher": "Springer Science and Business Media LLC",
  "ris": "https://research.draconitic.com/paper/74s167mt67qm1.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:18:01Z",
      "native_id": "10.1007/jhep10(2026)045",
      "source": "crossref",
      "url": "https://link.springer.com/10.1007/JHEP10(2026)045"
    }
  ],
  "subjects": [
    {
      "field": "physics",
      "origin": "openalex:3106|Quantum Chromodynamics and Particle Interactions",
      "subfield": "high-energy"
    }
  ],
  "title": "The a1(1420) in a unitary coupled-channel three-body approach",
  "title_text": "The a1(1420) in a unitary coupled-channel three-body approach",
  "type": "peer-reviewed",
  "updated_at": "2026-10-30T12:18:01Z",
  "url": "https://research.draconitic.com/paper/74s167mt67qm1",
  "venue": "Journal of High Energy Physics",
  "versions": [
    {
      "doi": "10.48550/arxiv.2606.24709",
      "pid": "fjg7s3yr65ecw",
      "relation": "preprint",
      "title": "The $a_1(1420)$ in a Unitary Coupled-Channel Three-Body Approach",
      "venue": "arXiv"
    }
  ]
}