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Search for Lepton-Flavor-Violating Decay Modes B0→KS0τ±ℓ∓ with Hadronic B Tagging at Belle and Belle II

I. Adachi, K. Adamczyk, L. Aggarwal, H. Ahmed, H. Aihara, N. Akopov, M. Alhakami, A. Aloisio, N. Althubiti et al. (Belle and Belle II Collaborations)

N. Althubiti, N. Anh Ky, D. M. Asner, H. Atmacan, V. Aushev, M. Aversano, R. Ayad, V. Babu, H. Bae, N. K. Baghel, S. Bahinipati, P. Bambade, Sw. Banerjee, S. Bansal, M. Barrett, M. Bartl, J. Baudot, A. Baur, A. Beaubien, F. Becherer, J. Becker, J. V. Bennett, F. U. Bernlochner, V. Bertacchi, M. Bertemes, E. Bertholet, M. Bessner, S. Bettarini, V. Bhardwaj, B. Bhuyan, F. Bianchi, D. Biswas, A. Bobrov, D. Bodrov, A. Bolz, A. Boschetti, A. Bozek, M. Bračko, P. Branchini, R. A. Briere, T. E. Browder, A. Budano, S. Bussino, Q. Campagna, M. Campajola, L. Cao, G. Casarosa, C. Cecchi, J. Cerasoli, M.-C. Chang, P. Chang, R. Cheaib, P. Cheema, B. G. Cheon, K. Chilikin, K. Chirapatpimol, H.-E. Cho, K. Cho, S.-J. Cho, S.-K. Choi, S. Choudhury, J. Cochran, L. Corona, J. X. Cui, E. De La Cruz-Burelo, S. A. De La Motte, G. de Marino, G. De Nardo, G. De Pietro, R. de Sangro, M. Destefanis, S. Dey, R. Dhamija, A. Di Canto, F. Di Capua, J. Dingfelder, Z. Doležal, I. Domínguez Jiménez, T. V. Dong, X. Dong, M. Dorigo, D. Dossett, S. Dubey, K. Dugic, G. Dujany, P. Ecker, P. Feichtinger, T. Ferber, T. Fillinger, C. Finck, G. Finocchiaro, A. Fodor, F. Forti, B. G. Fulsom, A. Gabrielli, E. Ganiev, M. Garcia-Hernandez, R. Garg, G. Gaudino, V. Gaur, A. Gaz, A. Gellrich, G. Ghevondyan, D. Ghosh, H. Ghumaryan, G. Giakoustidis, R. Giordano, A. Giri, P. Gironella Gironell, A. Glazov, B. Gobbo, R. Godang, O. Gogota, P. Goldenzweig, W. Gradl, S. Granderath, E. Graziani, D. Greenwald, Z. Gruberová, Y. Guan, K. Gudkova, I. Haide, Y. Han, T. Hara, C. Harris, K. Hayasaka, H. Hayashii, S. Hazra, C. Hearty, M. T. Hedges, A. Heidelbach, I. Heredia de la Cruz, M. Hernández Villanueva, T. Higuchi, M. Hoek, M. Hohmann, R. Hoppe, P. Horak, C.-L. Hsu, T. Humair, T. Iijima, K. Inami, G. Inguglia, N. Ipsita, A. Ishikawa, R. Itoh, M. Iwasaki, D. Jacobi, W. W. Jacobs, D. E. Jaffe, E.-J. Jang, Q. P. Ji, S. Jia, Y. Jin, A. Johnson, K. K. Joo, H. Junkerkalefeld, M. Kaleta, A. B. Kaliyar, J. Kandra, K. H. Kang, S. Kang, G. Karyan, T. Kawasaki, F. Keil, C. Ketter, C. Kiesling, C.-H. Kim, D. Y. Kim, J.-Y. Kim, K.-H. Kim, Y.-K. Kim, K. Kinoshita, P. Kodyš, T. Koga, S. Kohani, K. Kojima, A. Korobov, S. Korpar, E. Kovalenko, R. Kowalewski, P. Križan, P. Krokovny, T. Kuhr, Y. Kulii, D. Kumar, R. Kumar, K. Kumara, T. Kunigo, A. Kuzmin, Y.-J. Kwon, S. Lacaprara, Y.-T. Lai, K. Lalwani, T. Lam, L. Lanceri, J. S. Lange, T. S. Lau, M. Laurenza, R. Leboucher, F. R. Le Diberder, M. J. Lee, C. Lemettais, P. Leo, P. M. Lewis, C. Li, L. K. Li, Q. M. Li, W. Z. Li, Y. Li, Y. B. Li, Y. P. Liao, J. Libby, J. Lin, S. Lin, M. H. Liu, Q. Y. Liu, Y. Liu, Z. Q. Liu, D. Liventsev, S. Longo, T. Lueck, T. Luo, C. Lyu, Y. Ma, C. Madaan, M. Maggiora, S. P. Maharana, R. Maiti, G. Mancinelli, R. Manfredi, E. Manoni, M. Mantovano, S. Marcello, C. Marinas, C. Martellini, A. Martens, A. Martini, T. Martinov, L. Massaccesi, M. Masuda, D. Matvienko, S. K. Maurya, M. Maushart, J. A. McKenna, R. Mehta, F. Meier, D. Meleshko, M. Merola, C. Miller, M. Mirra, S. Mitra, K. Miyabayashi, H. Miyake, G. B. Mohanty, S. Mondal, S. Moneta, H.-G. Moser, R. Mussa, I. Nakamura, K. R. Nakamura, M. Nakao, Y. Nakazawa, M. Naruki, Z. Natkaniec, A. Natochii, M. Nayak, G. Nazaryan, M. Neu, S. Nishida, S. Ogawa, H. Ono, Y. Onuki, F. Otani, G. Pakhlova, E. Paoloni, S. Pardi, K. Parham, H. Park, J. Park, K. Park, S.-H. Park, B. Paschen, A. Passeri, S. Patra, T. K. Pedlar, I. Peruzzi, R. Peschke, R. Pestotnik, M. Piccolo, L. E. Piilonen, P. L. M. Podesta-Lerma, T. Podobnik, S. Pokharel, C. Praz, S. Prell, E. Prencipe, M. T. Prim, I. Prudiiev, H. Purwar, P. Rados, G. Raeuber, S. Raiz, N. Rauls, K. Ravindran, J. U. Rehman, M. Reif, S. Reiter, M. Remnev, L. Reuter, D. Ricalde Herrmann, I. Ripp-Baudot, G. Rizzo, S. H. Robertson, M. Roehrken, J. M. Roney, A. Rostomyan, N. Rout, D. A. Sanders, S. Sandilya, L. Santelj, V. Savinov, B. Scavino, S. Schneider, G. Schnell, C. Schwanda, Y. Seino, A. Selce, K. Senyo, J. Serrano, M. E. Sevior, C. Sfienti, W. Shan, C. Sharma, X. D. Shi, T. Shillington, T. Shimasaki, J.-G. Shiu, D. Shtol, A. Sibidanov, F. Simon, J. B. Singh, J. Skorupa, R. J. Sobie, M. Sobotzik, A. Soffer, A. Sokolov, E. Solovieva, S. Spataro, B. Spruck, W. Song, M. Starič, P. Stavroulakis, S. Stefkova, R. Stroili, J. Strube, Y. Sue, M. Sumihama, K. Sumisawa, W. Sutcliffe, N. Suwonjandee, H. Svidras, M. Takahashi, M. Takizawa, U. Tamponi, K. Tanida, F. Tenchini, A. Thaller, O. Tittel, R. Tiwary, E. Torassa, K. Trabelsi, I. Tsaklidis, I. Ueda, T. Uglov, K. Unger, Y. Unno, K. Uno, S. Uno, P. Urquijo, Y. Ushiroda, S. E. Vahsen, R. van Tonder, K. E. Varvell, M. Veronesi, A. Vinokurova, V. S. Vismaya, L. Vitale, V. Vobbilisetti, R. Volpe, M. Wakai, S. Wallner, M.-Z. Wang, Z. Wang, A. Warburton, M. Watanabe, S. Watanuki, C. Wessel, J. Wiechczynski, E. Won, X. P. Xu, B. D. Yabsley, S. Yamada, W. Yan, J. Yelton, J. H. Yin, K. Yoshihara, C. Z. Yuan, J. Yuan, L. Zani, F. Zeng, B. Zhang, J. S. Zhou, Q. D. Zhou, L. Zhu, V. I. Zhukova, and R. Žlebčík (Belle and Belle II Collaborations)

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Phys. Rev. Lett. 135, 041801 – Published 25 July, 2025

DOI: https://doi.org/10.1103/yzvh-v3hm

Abstract

We present the first search for the lepton-flavor-violating decay modes B0→KS0τ±ℓ∓ (ℓ=μ,e) using the 711 and 365  fb−1 data samples recorded by the Belle and Belle II detectors, respectively. We use a hadronic B-tagging technique to fully reconstruct a B meson and search for signal decays in the system recoiling against the tagged meson, considering τ decays to either light leptons, one charged hadron, or one charged hadron and a neutral pion. We find no evidence for B0→KS0τ±ℓ∓ decays and set 90% confidence level upper limits on the branching fractions in the range of [0.8,3.6]×10−5.

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17 July, 2026

Correction: Unnecessary labels have been removed from the figures.

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Phys. Rev. Lett. 135, 041801– Published 25 July, 2025
  • Received 4 January 2025
  • Revised 13 April 2025
  • Accepted 30 May 2025
  • Corrected 17 July 2026
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