Journal ArticleSearch for lepton-flavor-violating τ− → μ−μ+μ− decays at Belle IIAdachi, I; Aggarwal, L; Aihara, H; Akopov, N; Aloisio, A; Althubiti, N; Anh_Ky, N; Asner, D M; Atmacan, H; Aushev, V; Aversano, M; Ayad, R; Babu, V; Bae, H; Bahinipati, S; Bambade, P; Banerjee, Sw; Bansal, S; Barrett, M; Baudot, J; Baur, A; Beaubien, A; Becherer, F; Becker, J; Bennett, J V; Bernlochner, F U; Bertacchi, V; Bertemes, M; Bertholet, E; Bessner, M; Bettarini, S; Bianchi, F; Bierwirth, L; Bilka, T; Biswas, D; Bobrov, A; Bodrov, D; Bolz, A; Borah, J; Boschetti, A; Bozek, A; Bračko, M; Branchini, P; Browder, T E; Budano, A; Bussino, S; Campagna, Q; Campajola, M; Cao, L; Casarosa, G; Cecchi, C; Cerasoli, J; Chang, M-C; Chang, P; Cheaib, R; Cheema, P; Chen, C; Cheon, B G; Chilikin, K; Chirapatpimol, K; Cho, H-E; Cho, K; Cho, S-J; Choi, S-K; Choudhury, S; Cochran, J; Corona, L; Cui, J X; Das, S; Dattola, F; De_La_Cruz-Burelo, E; De_La_Motte, S A; De_Nardo, G; De_Nuccio, M; De_Pietro, G; de_Sangro, R; Destefanis, M; Dey, S; Dhamija, R; Di_Canto, A; Di_Capua, F; Dingfelder, J; Doležal, Z; Domínguez_Jiménez, I; Dong, T V; Dorigo, M; Dorner, D; Dort, K; Dossett, D; Dreyer, S; Dubey, S; Dugic, K; Dujany, G; Ecker, P; Eliachevitch, M; Feichtinger, P; Ferber, T; Ferlewicz, D; Fillinger, T; Finck, C; Finocchiaro, G; Fodor, A; Forti, F; Frey, A; Fulsom, B G; Gabrielli, A; Ganiev, E; Garcia-Hernandez, M; Garg, R; Gaudino, G; Gaur, V; Gaz, A; Gellrich, A; Ghevondyan, G; Ghosh, D; Ghumaryan, H; Giakoustidis, G; Giordano, R; Giri, A; Glazov, A; Gobbo, B; Godang, R; Gogota, O; Goldenzweig, P; Gradl, W; Grammatico, T; Granderath, S; Graziani, E; Greenwald, D; Gruberová, Z; Gu, T; Guan, Y; Gudkova, K; Halder, S; Han, Y; Hara, T; Harris, C; Hayasaka, K; Hayashii, H; Hazra, S; Hearty, C; Hedges, M T; Heidelbach, A; Heredia_de_la_Cruz, I; Hernández_Villanueva, M; Higuchi, T; Hoek, M; Hohmann, M; Horak, P; Hsu, C-L; Humair, T; Iijima, T; Inami, K; Inguglia, G; Ipsita, N; Ishikawa, A; Itoh, R; Iwasaki, M; Jacobs, W W; Jaffe, D E; Jang, E-J; Ji, Q P; Jia, S; Jin, Y; Junkerkalefeld, H; Kaleta, M; Kalita, D; Kaliyar, A B; Kandra, J; Kang, K H; Kang, S; Karyan, G; Kawasaki, T; Keil, F; Kiesling, C; Kim, C-H; Kim, D Y; Kim, K-H; Kim, Y-K; Kindo, H; Kinoshita, K; Kodyš, P; Koga, T; Kohani, S; Kojima, K; Konno, T; Korobov, A; Korpar, S; Kovalenko, E; Kowalewski, R; Kraetzschmar, T_M G; Križan, P; Krokovny, P; Kuhr, T; Kulii, Y; Kumar, J; Kumar, M; Kumar, R; Kumara, K; Kunigo, T; Kuzmin, A; Kwon, Y-J; Lacaprara, S; Lalwani, K; Lam, T; Lanceri, L; Lange, J S; Laurenza, M; Lautenbach, K; Leboucher, R; Le_Diberder, F R; Lee, M J; Leo, P; Lemettais, C; Levit, D; Lewis, P M; Li, L K; Li, S X; Li, Y; Li, Y B; Libby, J; Liu, M H; Liu, Q Y; Liu, Y; Liu, Z Q; Liventsev, D; Longo, S; Lueck, T; Lyu, C; Ma, Y; Maggiora, M; Maharana, S P; Maiti, R; Maity, S; Mancinelli, G; Manfredi, R; Manoni, E; Mantovano, M; Marcantonio, D; Marcello, S; Marinas, C; Martellini, C; Martini, A; Martinov, T; Massaccesi, L; Masuda, M; Matsuoka, K; Matvienko, D; Maurya, S K; McKenna, J A; Mehta, R; Meier, F; Merola, M; Metzner, F; Miller, C; Mirra, M; Mitra, S; Miyabayashi, K; Mohanty, G B; Mondal, S; Moneta, S; Moser, H-G; Mrvar, M; Mussa, R; Nakamura, I; Nakamura, K R; Nakao, M; Nakazawa, Y; Narimani_Charan, A; Naruki, M; Narwal, D; Natkaniec, Z; Natochii, A; Nayak, L; Nayak, M; Nazaryan, G; Neu, M; Niebuhr, C; Ninkovic, J; Nishida, S; Ogawa, S; Onishchuk, Y; Ono, H; Otani, F; Pakhlov, P; Pakhlova, G; Pardi, S; Parham, K; Park, H; Park, J; Park, S-H; Paschen, B; Passeri, A; Patra, S; Paul, S; Pedlar, T K; Peschke, R; Pestotnik, R; Piccolo, M; Piilonen, L E; Pinna_Angioni, G; Podesta-Lerma, P_L M; Podobnik, T; Pokharel, S; Praz, C; Prell, S; Prencipe, E; Prim, M T; Prudiev, I; Purwar, H; Rados, P; Raeuber, G; Raiz, S; Rauls, N; Reif, M; Reiter, S; Reuter, L; Ripp-Baudot, I; Rizzo, G; Robertson, S H; Roehrken, M; Roney, J M; Rostomyan, A; Rout, N; Russo, G; Sanders, D A; Sandilya, S; Santelj, L; Sato, Y; Savinov, V; Scavino, B; Schneider, S; Schwanda, C; Schwickardi, M; Seino, Y; Selce, A; Senyo, K; Serrano, J; Sevior, M E; Sfienti, C; Shan, W; Sharma, C; Shen, C P; Shi, X D; Shillington, T; Shimasaki, T; Shiu, J-G; Shtol, D; Sibidanov, A; Simon, F; Singh, J B; Skorupa, J; Smith, K; Sobie, R J; Sobotzik, M; Soffer, A; Sokolov, A; Solovieva, E; Spataro, S; Spruck, B; Starič, M; Stavroulakis, P; Stefkova, S; Stroili, R; Sue, Y; Sumihama, M; Sumisawa, K; Sutcliffe, W; Suwonjandee, N; Svidras, H; Takahashi, M; Takizawa, M; Tamponi, U; Tanaka, S; Tanida, K; Tenchini, F; Thaller, A; Tittel, O; Tiwary, R; Tonelli, D; Torassa, E; Trabelsi, K; Tsaklidis, I; Ueda, I; Uglov, T; Unger, K; Unno, Y; Uno, K; Uno, S; Urquijo, P; Ushiroda, Y; Vahsen, S E; van_Tonder, R; Varvell, K E; Veronesi, M; Vinokurova, A; Vismaya, V S; Vitale, L; Vobbilisetti, V; Volpe, R; Vossen, A; Wach, B; Wakai, M; Wallner, S; Wang, E; Wang, M-Z; Wang, X L; Wang, Z; Warburton, A; Watanabe, M; Watanuki, S; Wessel, C; Xu, X P; Yabsley, B D; Yamada, S; Yan, W; Yang, S B; Yelton, J; Yin, J H; Yook, Y M; Yoshihara, K; Yuan, C Z; Zani, L; Zeng, F; Zhang, B; Zhang, Y; Zhilich, V; Zhou, Q D; Zhou, X Y; Zhukova, V I; Žlebčík, RThe_Belle_II_collaboration<title>A<sc>bstract</sc></title> <p>We present the result of a search for the charged-lepton-flavor violating decay<italic>τ</italic>^{<italic>−</italic>}→<italic>μ</italic>^{<italic>−</italic>}<italic>μ</italic>⁺<italic>μ</italic>^{<italic>−</italic>}using a 424 fb^{<italic>−</italic>1}sample of data recorded by the Belle II experiment at the SuperKEKB<italic>e</italic>⁺<italic>e</italic>^{<italic>−</italic>}collider. The selection of<italic>e</italic>⁺<italic>e</italic>^{<italic>−</italic>}→<italic>τ</italic>⁺<italic>τ</italic>^{<italic>−</italic>}events is based on an inclusive reconstruction of the non-signal tau decay, and on a boosted decision tree to suppress background. We observe one signal candidate, which is compatible with the expectation from background processes. We set a 90% confidence level upper limit of 1<italic>.</italic>9<italic>×</italic>10^{<italic>−</italic>8}on the branching fraction of the<italic>τ</italic>^{<italic>−</italic>}<italic>→ μ</italic>^{<italic>−</italic>}<italic>μ</italic>⁺<italic>μ</italic>^{<italic>−</italic>}decay, which is the most stringent bound to date.</p>Springer2024-09-0110613133Journal of High Energy Physics202491029-8479https://doi.org/10.1007/JHEP09(2024)0622209481National Science Foundation