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arXiv · 2505.08418

Search for lepton flavor-violating decay modes $B^0 \to K^{\ast 0}\tau^\pm\ell^\mp$ ($\ell = e,\mu$) with hadronic B-tagging at Belle and Belle II

Belle·Belle II Collaborations·:·I. Adachi·Y. Ahn·H. Aihara·N. Akopov·S. Alghamdi·M. Alhakami·A. Aloisio·K. Amos·M. Angelsmark·N. Anh Ky·C. Antonioli·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·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·B. Bhuyan·F. Bianchi·T. Bilka·D. Biswas·A. Bobrov·D. Bodrov·J. Borah·A. Boschetti·A. Bozek·M. Bračko·P. Branchini·R. A. Briere·T. E. Browder·A. Budano·S. Bussino·M. Campajola·L. Cao·G. Casarosa·C. Cecchi·M. -C. Chang·P. Cheema·B. G. Cheon·K. Chilikin·J. Chin·H. -E. Cho·K. Cho·S. -J. Cho·S. -K. Choi·S. Choudhury·I. Consigny·L. Corona·J. X. Cui·E. De La Cruz-Burelo·S. A. De La Motte·G. de Marino·G. De Pietro·R. de Sangro·M. Destefanis·A. Di Canto·J. Dingfelder·Z. Doležal·I. Domínguez Jiménez·T. V. Dong·X. Dong·M. Dorigo·G. Dujany·P. Ecker·D. Epifanov·R. Farkas·P. Feichtinger·T. Ferber·T. Fillinger·C. Finck·G. Finocchiaro·F. Forti·A. Frey·B. G. Fulsom·A. Gale·E. Ganiev·M. Garcia-Hernandez·R. Garg
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Abstract

We present the results of a search for the charged-lepton-flavor violating decays $B^0 \rightarrow K^{*0}\tau^\pm \ell^{\mp}$, where $\ell^{\mp}$ is either an electron or a muon. The results are based on 365 fb$^{-1}$ and 711 fb$^{-1}$ datasets collected with the Belle II and Belle detectors, respectively. We use an exclusive hadronic $B$-tagging technique, and search for a signal decay in the system recoiling against a fully reconstructed $B$ meson. We find no evidence for $B^0 \rightarrow K^{*0}\tau^\pm \ell^{\mp}$ decays and set upper limits on the branching fractions in the range of $(2.9-6.4)\times10^{-5}$ at 90% confidence level.

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Belle, Belle II Collaborations, :, I. Adachi, Y. Ahn, H. Aihara, N. Akopov, S. Alghamdi, M. Alhakami, A. Aloisio, K. Amos, M. Angelsmark, N. Anh Ky, C. Antonioli, 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, 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, B. Bhuyan, F. Bianchi, T. Bilka, D. Biswas, A. Bobrov, D. Bodrov, J. Borah, A. Boschetti, A. Bozek, M. Bračko, P. Branchini, R. A. Briere, T. E. Browder, A. Budano, S. Bussino, M. Campajola, L. Cao, G. Casarosa, C. Cecchi, M. -C. Chang, P. Cheema, B. G. Cheon, K. Chilikin, J. Chin, H. -E. Cho, K. Cho, S. -J. Cho, S. -K. Choi, S. Choudhury, I. Consigny, L. Corona, J. X. Cui, E. De La Cruz-Burelo, S. A. De La Motte, G. de Marino, G. De Pietro, R. de Sangro, M. Destefanis, A. Di Canto, J. Dingfelder, Z. Doležal, I. Domínguez Jiménez, T. V. Dong, X. Dong, M. Dorigo, G. Dujany, P. Ecker, D. Epifanov, R. Farkas, P. Feichtinger, T. Ferber, T. Fillinger, C. Finck, G. Finocchiaro, F. Forti, A. Frey, B. G. Fulsom, A. Gale, E. Ganiev, M. Garcia-Hernandez, R. Garg. 2025-05-13. Search for lepton flavor-violating decay modes $B^0 \to K^{\ast 0}\tau^\pm\ell^\mp$ ($\ell = e,\mu$) with hadronic B-tagging at Belle and Belle II. https://doi.org/10.1007/jhep08(2025)184

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