{
  "abstract": "Branching fractions of $η$ and $η'(958)$ anomalous decays are measured using $pp$ collision data at a center-of-mass energy of $\\sqrt{s}=13\\,\\text{TeV}$ collected by the LHCb experiment and corresponding to an integrated luminosity of $5.4\\,\\text{fb}^{-1}$. The measured values and upper limits are \\begin{align*} \\cal{B}(η\\toμ^+μ^-) &= (5.02\\pm0.14\\pm0.18\\pm0.26)\\times10^{-6} , \\\\ \\cal{B}(η'(958)\\toμ^+μ^-) &<1.9\\times10^{-7}\\textrm{ at 90% CL} , \\\\ \\cal{B}(η\\toπ^+π^-μ^+μ^-) &<5.4\\times10^{-7}\\textrm{ at 90% CL}, \\\\ \\cal{B}(η'(958)\\toπ^+π^-μ^+μ^-) &= (2.73\\pm0.14\\pm0.13\\pm0.14)\\times10^{-5} , \\end{align*} where the uncertainties are, respectively, statistical, systematic, and due to the external branching fraction of the $ϕ(1020)\\toμ^+μ^-$ decay, which is used for normalization. This marks the first experimental search for the $η'(958)$ decay, and the most precise measurement of the branching fraction $\\cal{B}(η\\toμ^+μ^-)$ to date.",
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  "arxiv": "2609.02973",
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    {
      "name": "Roel Aaij"
    },
    {
      "name": "Ahmed Sameh Wagih Abdelmotteleb"
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      "name": "Ziad Ajaltouni"
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    {
      "name": "Kazuyoshi Akiba"
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    {
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      "name": "Renaud Amalric"
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    {
      "name": "Sandra Amato"
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    {
      "name": "Jake Lewis Amey"
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    {
      "name": "Yasmine Amhis"
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    {
      "name": "Liupan An"
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    {
      "name": "Lucio Anderlini"
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    {
      "name": "Martin Andersson"
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    {
      "name": "Pasquale Andreola"
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    {
      "name": "Mirco Andreotti"
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    {
      "name": "Sergio Andres Estrada"
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    {
      "name": "Alessia Anelli"
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    {
      "name": "Dong Ao"
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    {
      "name": "Carolina Arata"
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    {
      "name": "Irene Bachiller Perea"
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    {
      "name": "Sebastian Bachmann"
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    {
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    {
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    {
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    {
      "name": "Haoran Bao"
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    {
      "name": "Juan Baptista de Souza Leite"
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    {
      "name": "Carlos Javier Barbero Pretel"
    },
    {
      "name": "Matteo Barbetti"
    },
    {
      "name": "Ivanildo Rui Barbosa"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/fd673hsc8g7ed.bib",
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  "doi": "10.48550/arxiv.2609.02973",
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  "pdf_url": "https://arxiv.org/pdf/2609.02973",
  "pmcid": null,
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  "published": "2026-09-04",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/fd673hsc8g7ed.ris",
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      "first_seen": "2026-10-30T12:17:37Z",
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  "subjects": [
    {
      "field": "physics",
      "origin": "arxiv:hep-ex",
      "subfield": "high-energy"
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  "title": "Branching fraction measurements of $η$ and $η^\\prime(958)$ anomalous decays",
  "title_text": "Branching fraction measurements of η and η^′(958) anomalous decays",
  "type": "preprint",
  "updated_at": "2026-10-30T12:19:14Z",
  "url": "https://research.draconitic.com/paper/fd673hsc8g7ed",
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