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Search for the Decay B+→K+τ+τ− Using Data from the Belle and Belle II Experiments

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

N. Akopov, 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 Marino, 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, M. Dorigo, K. Dugic, G. Dujany, P. Ecker, J. Eppelt, R. Farkas, 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, L. Gärtner, G. Gaudino, V. Gaur, V. Gautam, A. Gaz, A. Gellrich, G. Ghevondyan, D. Ghosh, R. Giordano, A. Giri, P. Gironella Gironell, A. Glazov, B. Gobbo, R. Godang, O. Gogota, P. Goldenzweig, W. Gradl, E. Graziani, D. Greenwald, Y. Guan, K. Gudkova, I. Haide, H. Haigh, Y. Han, H. Hayashii, S. Hazra, C. Hearty, 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, C. Kim, 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, L. Lanceri, 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, Z. Liptak, V. Lisovskyi, M. H. Liu, Q. Y. Liu, Y. Liu, Z. Q. 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, Y. Nakazawa, M. Naruki, Z. Natkaniec, A. Natochii, M. Nayak, M. Neu, M. Niiyama, S. Nishida, R. Nomaru, S. Ogawa, R. Okubo, H. Ono, Y. Onuki, 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, E. Prencipe, M. T. Prim, S. Privalov, I. Prudiiev, 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, C. Schmitt, S. Schneider, G. Schnell, K. Schoenning, C. Schwanda, A. J. Schwartz, 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, B. Shwartz, 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, J. Strube, M. Sumihama, N. Suwonjandee, M. Takahashi, M. Takizawa, S. S. Tang, K. Tanida, F. Tenchini, F. Testa, A. Thaller, T. Tien Manh, O. Tittel, R. Tiwary, D. Tonelli, E. Torassa, K. Trabelsi, F. F. Trantou, 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, 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, 051805 – Published 30 July, 2026

DOI: https://doi.org/10.1103/12f4-z51q

Abstract

We report a search for the rare decay B+→K+τ+τ− using 1.2×109  ϒ(4S) mesons produced near threshold in electron-positron collisions and collected by the Belle and Belle II experiments. We fully reconstruct the hadronic decay of one B meson produced in the ϒ(4S)→B+B− decay, and search for B±→K±τ+τ− candidates among the remaining collision products, reconstructing a charged kaon and leptonic decays of the τ leptons. We optimize the selection for best sensitivity and look for an excess over background at low values of the residual energy detected in the calorimeter after full event reconstruction. We observe no significant excess and set the limit B(B+→K+τ+τ−)<0.56×10−3 at the 90% confidence level, improving on the only previous result by a factor of four.

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Phys. Rev. Lett. 137, 051805– Published 30 July, 2026
  • Received 27 March 2026
  • Accepted 17 June 2026
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP3.

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