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Searches for Charged-Lepton-Flavor Violation in χbJ(1P) Decays

M. Abumusabh, I. Adachi, A. Aggarwal, L. Aggarwal, H. Ahmed, Y. Ahn, H. Aihara, N. Akopov, S. Alghamdi et al. (Belle and Belle II Collaborations)

S. Alghamdi, M. Alhakami, A. Aloisio, N. Althubiti, K. Amos, M. Angelsmark, N. Anh Ky, C. Antonioli, D. M. Asner, H. Atmacan, T. Aushev, R. Ayad, V. Babu, H. Bae, N. K. Baghel, S. Bahinipati, P. Bambade, Sw. Banerjee, 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, F. Bianchi, T. Bilka, D. Biswas, A. Bobrov, D. Bodrov, A. Bondar, G. Bonvicini, J. Borah, 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, M.-C. Chang, P. Chang, P. Cheema, L. Chen, B. G. Cheon, C. Cheshta, H. Chetri, K. Chilikin, K. Chirapatpimol, H.-E. Cho, K. Cho, S.-J. Cho, S.-K. Choi, S. Choudhury, S. Chutia, J. Cochran, J. A. Colorado-Caicedo, I. Consigny, L. Corona, J. X. Cui, E. De La Cruz-Burelo, S. A. De La Motte, G. De Nardo, G. De Pietro, R. de Sangro, M. Destefanis, S. Dey, R. Dhayal, A. Di Canto, J. Dingfelder, Z. Doležal, I. Domínguez Jiménez, T. V. Dong, X. Dong, G. Dujany, P. Ecker, D. Epifanov, J. Eppelt, R. Farkas, P. Feichtinger, T. Ferber, T. Fillinger, C. Finck, G. Finocchiaro, F. Forti, A. Frey, B. G. Fulsom, A. Gabrielli, A. Gale, E. Ganiev, M. Garcia-Hernandez, R. Garg, G. Gaudino, V. Gaur, V. Gautam, A. Gellrich, G. Ghevondyan, R. Giordano, A. Giri, P. Gironella Gironell, B. Gobbo, R. Godang, P. Goldenzweig, W. Gradl, E. Graziani, D. Greenwald, Y. Guan, K. Gudkova, I. Haide, Y. Han, H. Hayashii, S. Hazra, M. T. Hedges, A. Heidelbach, G. Heine, I. Heredia de la Cruz, M. Hernández Villanueva, T. Higuchi, M. Hoek, M. Hohmann, R. Hoppe, P. Horak, X. T. Hou, C.-L. Hsu, T. Humair, T. Iijima, K. Inami, G. Inguglia, N. Ipsita, A. Ishikawa, R. Itoh, M. Iwasaki, P. Jackson, D. Jacobi, W. W. Jacobs, E.-J. Jang, Q. P. Ji, S. Jia, Y. Jin, A. Johnson, J. Kandra, K. H. Kang, S. Kang, G. Karyan, F. Keil, C. Ketter, C. Kiesling, D. Y. Kim, H. Kim, J.-Y. Kim, K.-H. Kim, H. Kindo, K. Kinoshita, P. Kodyš, T. Koga, S. Kohani, A. Korobov, S. Korpar, E. Kovalenko, R. Kowalewski, P. Križan, P. Krokovny, T. Kuhr, Y. Kulii, D. Kumar, J. Kumar, R. Kumar, K. Kumara, T. Kunigo, A. Kuzmin, Y.-J. Kwon, S. Lacaprara, T. Lam, J. S. Lange, T. S. Lau, M. Laurenza, R. Leboucher, F. R. Le Diberder, H. Lee, M. J. Lee, C. Lemettais, P. Leo, P. M. Lewis, C. Li, H.-J. 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. Liu, D. Liventsev, S. Longo, A. Lozar, T. Lueck, C. Lyu, J. L. Ma, Y. Ma, M. Maggiora, S. P. Maharana, R. Maiti, G. Mancinelli, R. Manfredi, E. Manoni, M. Mantovano, D. Marcantonio, S. Marcello, M. Marfoli, C. Marinas, C. Martellini, A. Martens, T. Martinov, L. Massaccesi, M. Masuda, D. Matvienko, S. K. Maurya, M. Maushart, J. A. McKenna, Z. Mediankin Gruberová, R. Mehta, F. Meier, D. Meleshko, M. Merola, C. Miller, M. Mirra, K. Miyabayashi, H. Miyake, R. Mizuk, G. B. Mohanty, S. Moneta, A. L. Moreira de Carvalho, H.-G. Moser, Th. Muller, R. Mussa, I. Nakamura, M. Nakao, H. Nakazawa, Y. Nakazawa, M. Naruki, Z. Natkaniec, A. Natochii, M. Nayak, M. Neu, M. Niiyama, S. Nishida, R. Nomaru, S. Ogawa, R. Okubo, H. Ono, F. Otani, P. Pakhlov, G. Pakhlova, A. Panta, S. Pardi, K. Parham, J. Park, K. Park, S.-H. Park, A. Passeri, S. Patra, S. Paul, T. K. Pedlar, R. Pestotnik, M. Piccolo, L. E. Piilonen, P. L. M. Podesta-Lerma, T. Podobnik, A. Prakash, C. Praz, S. Prell, M. T. Prim, H. Purwar, P. Rados, S. Raiz, K. Ravindran, J. U. Rehman, M. Reif, S. Reiter, L. Reuter, D. Ricalde Herrmann, I. Ripp-Baudot, G. Rizzo, S. H. Robertson, J. M. Roney, A. Rostomyan, N. Rout, S. Saha, L. Salutari, D. A. Sanders, S. Sandilya, L. Santelj, C. Santos, V. Savinov, B. Scavino, S. Schneider, G. Schnell, K. Schoenning, C. Schwanda, Y. Seino, K. Senyo, J. Serrano, M. E. Sevior, C. Sfienti, W. Shan, G. Sharma, C. P. Shen, X. D. Shi, T. Shillington, T. Shimasaki, J.-G. Shiu, D. Shtol, A. Sibidanov, F. Simon, J. Skorupa, R. J. Sobie, M. Sobotzik, A. Soffer, A. Sokolov, E. Solovieva, W. Song, S. Spataro, K. Špenko, B. Spruck, M. Starič, P. Stavroulakis, S. Stefkova, R. Stroili, M. Sumihama, N. Suwonjandee, M. Takahashi, M. Takizawa, U. Tamponi, S. S. Tang, K. Tanida, F. Tenchini, F. Testa, A. Thaller, T. Tien Manh, O. Tittel, R. Tiwary, E. Torassa, K. Trabelsi, F. F. Trantou, I. Tsaklidis, I. Ueda, K. Unger, Y. Unno, K. Uno, S. Uno, P. Urquijo, Y. Ushiroda, Y. V. Usov, S. E. Vahsen, R. van Tonder, K. E. Varvell, M. Veronesi, V. S. Vismaya, L. Vitale, V. Vobbilisetti, R. Volpe, M. Wakai, S. Wallner, M.-Z. Wang, A. Warburton, M. Watanabe, S. Watanuki, C. Wessel, E. Won, X. P. Xu, B. D. Yabsley, W. Yan, W. Yan, J. Yelton, K. Yi, J. H. Yin, K. Yoshihara, J. Yuan, Y. Yusa, L. Zani, F. Zeng, M. Zeyrek, B. Zhang, V. Zhilich, J. S. Zhou, Q. D. Zhou, L. Zhu, and R. Žlebčík (Belle and Belle II Collaborations)

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Phys. Rev. Lett. 137, 071803 – Published 12 August, 2026

DOI: https://doi.org/10.1103/1rj5-2wvr

Abstract

We report the first searches for charged-lepton-flavor violation in decays of χbJ(1P) (J=0, 1, and 2) to a pair of charged leptons using 158 million ϒ(2S) decays collected with the Belle detector in e+e− collisions at the KEKB collider. No significant signal is observed, and we set upper limits on the branching fractions for χbJ(1P) decays to e±μ∓ at the level of 10−6 and to e±τ∓ or μ±τ∓ at the level of 10−5. Limits on χb0(1P) decays are translated into bounds on the corresponding Wilson coefficients of scalar operators that mediate charged-lepton-flavor violation.

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Phys. Rev. Lett. 137, 071803– Published 12 August, 2026
  • Received 13 March 2026
  • Accepted 6 July 2026
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