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arXiv · 2311.07248

First Measurement of $R(X_{\tau/\ell})$ as an Inclusive Test of the $b \to c \tau \nu$ Anomaly

Belle II Collaboration·I. Adachi·K. Adamczyk·L. Aggarwal·H. Ahmed·H. Aihara·N. Akopov·A. Aloisio·D. M. Asner·H. Atmacan·T. Aushev·V. Aushev·M. Aversano·V. Babu·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·S. Bilokin·D. Biswas·A. Bobrov·D. Bodrov·A. Bolz·A. Bondar·A. Bozek·M. Bračko·P. Branchini·R. A. Briere·T. E. Browder·A. Budano·S. Bussino·M. Campajola·L. Cao·G. Casarosa·C. Cecchi·J. Cerasoli·M. -C. Chang·P. Chang·P. Cheema·B. G. Cheon·K. Chilikin·K. Chirapatpimol·H. -E. Cho·K. Cho·S. -J. Cho·S. -K. Choi·S. Choudhury·L. Corona·L. M. Cremaldi·F. Dattola·E. De La Cruz-Burelo·S. A. De La Motte·G. de Marino·G. De Nardo·M. De Nuccio·G. De Pietro·R. de Sangro·M. Destefanis·R. Dhamija·A. Di Canto·F. Di Capua·J. Dingfelder·Z. Doležal·T. V. Dong·M. Dorigo·K. Dort·S. Dreyer·S. Dubey·G. Dujany·P. Ecker·M. Eliachevitch·D. Epifanov·P. Feichtinger·T. Ferber·D. Ferlewicz·T. Fillinger·G. Finocchiaro·A. Fodor·F. Forti·A. Frey·B. G. Fulsom·E. Ganiev·M. Garcia-Hernandez·R. Garg
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Abstract

We measure the tau-to-light-lepton ratio of inclusive $B$-meson branching fractions $R(X_{\tau/\ell}) \equiv \mathcal{B}(B\to X \tau \nu)/\mathcal{B}(B \to X \ell \nu)$, where $\ell$ indicates an electron or muon, and thereby test the universality of charged-current weak interactions. We select events that have one fully reconstructed $B$ meson and a charged lepton candidate from $189~\mathrm{fb}^{-1}$ of electron-positron collision data collected with the Belle II detector. We find $R(X_{\tau/\ell}) = 0.228 \pm 0.016~(\mathrm{stat}) \pm 0.036~(\mathrm{syst})$, in agreement with standard-model expectations. This is the first direct measurement of $R(X_{\tau/\ell})$.

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Belle II Collaboration, I. Adachi, K. Adamczyk, L. Aggarwal, H. Ahmed, H. Aihara, N. Akopov, A. Aloisio, D. M. Asner, H. Atmacan, T. Aushev, V. Aushev, M. Aversano, V. Babu, 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, S. Bilokin, D. Biswas, A. Bobrov, D. Bodrov, A. Bolz, A. Bondar, A. Bozek, M. Bračko, P. Branchini, R. A. Briere, T. E. Browder, A. Budano, S. Bussino, M. Campajola, L. Cao, G. Casarosa, C. Cecchi, J. Cerasoli, M. -C. Chang, P. Chang, P. Cheema, B. G. Cheon, K. Chilikin, K. Chirapatpimol, H. -E. Cho, K. Cho, S. -J. Cho, S. -K. Choi, S. Choudhury, L. Corona, L. M. Cremaldi, F. Dattola, E. De La Cruz-Burelo, S. A. De La Motte, G. de Marino, G. De Nardo, M. De Nuccio, G. De Pietro, R. de Sangro, M. Destefanis, R. Dhamija, A. Di Canto, F. Di Capua, J. Dingfelder, Z. Doležal, T. V. Dong, M. Dorigo, K. Dort, S. Dreyer, S. Dubey, G. Dujany, P. Ecker, M. Eliachevitch, D. Epifanov, P. Feichtinger, T. Ferber, D. Ferlewicz, T. Fillinger, G. Finocchiaro, A. Fodor, F. Forti, A. Frey, B. G. Fulsom, E. Ganiev, M. Garcia-Hernandez, R. Garg. 2023-11-13. First Measurement of $R(X_{\tau/\ell})$ as an Inclusive Test of the $b \to c \tau \nu$ Anomaly. https://doi.org/10.1103/physrevlett.132.211804

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