<p>We report a search for the lepton-flavor-violating decays <i>τ</i><sup><i>±</i></sup> → <i>ℓ</i><sup><i>±</i></sup><i>α</i> (<i>ℓ</i> = <i>e</i>, <i>μ</i>), where <i>α</i> is an undetected spin-0 particle, such as an axion-like particle using 736 × 10<sup>6</sup> tau lepton pairs collected by the Belle detector at the KEKB asymmetric-energy <i>e</i><sup>+</sup><i>e</i><sup><i>−</i></sup> collider. We find no evidence of signal and obtain the most stringent upper limits on the branching fractions at 95% confidence level: <InlineEquation ID="IEq1"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13130_2025_27014_Article_IEq1.gif" Format="GIF" Height="14" Rendition="HTML" Resolution="72" Type="Linedraw" Width="16" /> </InlineMediaObject> <EquationSource Format="TEX">\(\mathcal{B}\)</EquationSource> </InlineEquation>(<i>τ</i><sup><i>±</i></sup><i> → e</i><sup><i>±</i></sup><i>α</i>) &lt; (0.4–6.4) <i>×</i> 10<sup><i>−</i>4</sup> and <InlineEquation ID="IEq2"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13130_2025_27014_Article_IEq1.gif" Format="GIF" Height="14" Rendition="HTML" Resolution="72" Type="Linedraw" Width="16" /> </InlineMediaObject> <EquationSource Format="TEX">\(\mathcal{B}\)</EquationSource> </InlineEquation>(<i>τ</i><sup><i>±</i></sup><i> → μ</i><sup><i>±</i></sup><i>α</i>) &lt; (0.2–3.5) <i>×</i> 10<sup><i>−</i>4</sup> at 95% confidence level for an <i>α</i> mass in the range 0.0 <i>≤ m</i><sub><i>α</i></sub><i> ≤</i> 1.6 GeV/<i>c</i><sup>2</sup>.</p>

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Search for lepton-flavor-violating tau decays to ℓα at Belle

  • K. Uno,
  • K. Hayasaka,
  • K. Inami,
  • H. Aihara,
  • R. Ayad,
  • Sw. Banerjee,
  • K. Belous,
  • J. Bennett,
  • M. Bessner,
  • D. Biswas,
  • D. Bodrov,
  • M. Bračko,
  • P. Branchini,
  • T. E. Browder,
  • A. Budano,
  • M. Campajola,
  • K. Cho,
  • S.-K. Choi,
  • Y. Choi,
  • S. Choudhury,
  • G. De Nardo,
  • G. De Pietro,
  • F. Di Capua,
  • J. Dingfelder,
  • Z. Doležal,
  • P. Ecker,
  • D. Epifanov,
  • T. Ferber,
  • B. G. Fulsom,
  • V. Gaur,
  • A. Giri,
  • P. Goldenzweig,
  • E. Graziani,
  • Y. Guan,
  • K. Gudkova,
  • C. Hadjivasiliou,
  • T. Hara,
  • H. Hayashii,
  • D. Herrmann,
  • C.-L. Hsu,
  • N. Ipsita,
  • A. Ishikawa,
  • R. Itoh,
  • M. Iwasaki,
  • W. W. Jacobs,
  • Y. Jin,
  • C. Kiesling,
  • C. H. Kim,
  • D. Y. Kim,
  • K.-H. Kim,
  • K. Kinoshita,
  • P. Kodyš,
  • A. Korobov,
  • S. Korpar,
  • E. Kovalenko,
  • P. Krokovny,
  • R. Kumar,
  • K. Kumara,
  • A. Kuzmin,
  • Y.-J. Kwon,
  • T. Lam,
  • L. K. Li,
  • Y. B. Li,
  • L. Li Gioi,
  • J. Libby,
  • D. Liventsev,
  • Y. Ma,
  • M. Masuda,
  • T. Matsuda,
  • D. Matvienko,
  • F. Meier,
  • M. Merola,
  • K. Miyabayashi,
  • G. B. Mohanty,
  • M. Nakao,
  • H. Nakazawa,
  • A. Natochii,
  • M. Niiyama,
  • S. Nishida,
  • S. Ogawa,
  • H. Ono,
  • S. Pardi,
  • J. Park,
  • S.-H. Park,
  • S. Patra,
  • S. Paul,
  • T. K. Pedlar,
  • L. E. Piilonen,
  • T. Podobnik,
  • S. Prell,
  • E. Prencipe,
  • M. T. Prim,
  • G. Russo,
  • S. Sandilya,
  • L. Santelj,
  • V. Savinov,
  • G. Schnell,
  • C. Schwanda,
  • Y. Seino,
  • K. Senyo,
  • W. Shan,
  • J.-G. Shiu,
  • B. Shwartz,
  • F. Simon,
  • J. B. Singh,
  • E. Solovieva,
  • M. Starič,
  • M. Sumihama,
  • M. Takizawa,
  • K. Tanida,
  • F. Tenchini,
  • K. Trabelsi,
  • S. Uehara,
  • T. Uglov,
  • Y. Unno,
  • S. Uno,
  • M.-Z. Wang,
  • E. Won,
  • B. D. Yabsley,
  • Y. Yook,
  • C. Z. Yuan,
  • L. Yuan,
  • Y. Yusa,
  • Z. P. Zhang,
  • V. Zhilich

摘要

We report a search for the lepton-flavor-violating decays τ±±α ( = e, μ), where α is an undetected spin-0 particle, such as an axion-like particle using 736 × 106 tau lepton pairs collected by the Belle detector at the KEKB asymmetric-energy e+e collider. We find no evidence of signal and obtain the most stringent upper limits on the branching fractions at 95% confidence level: \(\mathcal{B}\) (τ± → e±α) < (0.4–6.4) × 104 and \(\mathcal{B}\) (τ± → μ±α) < (0.2–3.5) × 104 at 95% confidence level for an α mass in the range 0.0 ≤ mα 1.6 GeV/c2.