{
  "abstract": "We propose a recoil-assisted strategy for vertexing displaced diphoton decays in $e^+e^-\\toγX$, $X\\toγγ$, using only one converted daughter photon. The initial state and recoil-photon momentum define the LLP flight line, whose closest approach to the converted-photon trajectory locates the decay vertex. This removes the need for a second conversion, making the conversion-related efficiency scale linearly rather than quadratically with the photon-conversion probability. For photophilic axionlike particles at Belle II, the existing $408$ fb$^{-1}$ data set could probe previously unconstrained parameter space near $m_a \\simeq 100$ MeV and $g_{aγγ} \\simeq 2 \\times 10^{-4}$ GeV$^{-1}$, improving leading bounds by almost an order of magnitude and testing the mass region below the $π^0$ mass, which the existing Belle II three-photon searches cannot access. With $50$ ab$^{-1}$, the reach extends to $m_a \\simeq 310$ MeV and $g_{aγγ}\\simeq2\\times10^{-5}$ GeV$^{-1}$.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": "2609.15324",
  "author_total": 2,
  "authors": [
    {
      "name": "Zeren Simon Wang"
    },
    {
      "name": "Yu Zhang"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/4hf92wts5j766.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2609.15324",
  "fulltext_url": null,
  "id": "4hf92wts5j766",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2609.15324",
  "language": null,
  "licence": "LicenseRef-arXiv-nonexclusive-1.0",
  "licence_label": "arXiv licence",
  "licence_source": "article",
  "licence_url": "http://arxiv.org/licenses/nonexclusive-distrib/1.0/",
  "metadata_licence": "CC0-1.0",
  "native_subjects": [
    [
      "arxiv",
      "hep-ex"
    ],
    [
      "arxiv",
      "hep-ph"
    ],
    [
      "openalex",
      "3106|Particle physics theoretical and experimental studies"
    ]
  ],
  "openalex": "W7213372581",
  "pdf_url": "https://arxiv.org/pdf/2609.15324",
  "pmcid": null,
  "pmid": null,
  "published": "2026-09-21",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/4hf92wts5j766.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:23:19Z",
      "native_id": "2609.15324",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2609.15324"
    }
  ],
  "subjects": [
    {
      "field": "physics",
      "origin": "arxiv:hep-ex",
      "subfield": "high-energy"
    }
  ],
  "title": "Vertexing displaced diphoton decays with recoil photons at Belle II",
  "title_text": "Vertexing displaced diphoton decays with recoil photons at Belle II",
  "type": "preprint",
  "updated_at": "2026-10-30T12:23:19Z",
  "url": "https://research.draconitic.com/paper/4hf92wts5j766",
  "venue": "arXiv",
  "versions": []
}