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arXiv · 2301.08266

A test of light-lepton universality in the rates of inclusive semileptonic $B$-meson decays at Belle II

Belle II Collaboration·L. Aggarwal·H. Ahmed·H. Aihara·N. Akopov·A. Aloisio·N. Anh Ky·D. M. Asner·H. Atmacan·T. Aushev·V. Aushev·H. Bae·S. Bahinipati·P. Bambade·Sw. Banerjee·S. Bansal·M. Barrett·J. Baudot·M. Bauer·A. Baur·A. Beaubien·J. Becker·J. V. Bennett·E. Bernieri·F. U. Bernlochner·V. Bertacchi·M. Bertemes·E. Bertholet·M. Bessner·S. Bettarini·V. Bhardwaj·B. Bhuyan·F. Bianchi·T. Bilka·S. Bilokin·D. Biswas·D. Bodrov·J. Borah·A. Bozek·M. Bračko·R. A. Briere·T. E. Browder·A. Budano·S. Bussino·M. Campajola·L. Cao·G. Casarosa·C. Cecchi·J. Cerasoli·M. -C. Chang·R. Cheaib·P. Cheema·V. Chekelian·B. G. Cheon·K. Chilikin·K. Chirapatpimol·H. -E. Cho·K. Cho·S. -J. Cho·S. -K. Choi·S. Choudhury·J. Cochran·L. Corona·S. Cunliffe·F. Dattola·E. De La Cruz-Burelo·S. A. De La Motte·G. De Nardo·G. De Pietro·R. de Sangro·M. Destefanis·R. Dhamija·F. Di Capua·J. Dingfelder·Z. Doležal·T. V. Dong·M. Dorigo·D. Dossett·S. Dreyer·S. Dubey·G. Dujany·P. Ecker·M. Eliachevitch·P. Feichtinger·T. Ferber·D. Ferlewicz·T. Fillinger·G. Finocchiaro·A. Fodor·F. Forti·A. Frey·B. G. Fulsom·A. Gabrielli·E. Ganiev·M. Garcia-Hernandez·G. Gaudino·V. Gaur·A. Gaz·A. Gellrich·G. Ghevondyan
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Abstract

We present the first measurement of the ratio of branching fractions of inclusive semileptonic $B$-meson decays, $R(X_{e/\mu}) = \mathcal{B}(B\to X \, e \, \nu) / \mathcal{B}(B\to X \, \mu \, \nu)$, a precision test of electron-muon universality, using data corresponding to $189\,\mathrm{fb}^{-1}$ from electron-positron collisions collected with the Belle II detector. In events where the partner $B$ meson is fully reconstructed, we use fits to the lepton momentum spectra above $1.3\,\mathrm{GeV}/c$ to obtain $R(X_{e/\mu}) = 1.007 \pm 0.009~(\mathrm{stat}) \pm 0.019~(\mathrm{syst})$, which is the most precise lepton-universality test of its kind and agrees with the standard-model expectation.

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Belle II Collaboration, L. Aggarwal, H. Ahmed, H. Aihara, N. Akopov, A. Aloisio, N. Anh Ky, D. M. Asner, H. Atmacan, T. Aushev, V. Aushev, H. Bae, S. Bahinipati, P. Bambade, Sw. Banerjee, S. Bansal, M. Barrett, J. Baudot, M. Bauer, A. Baur, A. Beaubien, J. Becker, J. V. Bennett, E. Bernieri, F. U. Bernlochner, V. Bertacchi, M. Bertemes, E. Bertholet, M. Bessner, S. Bettarini, V. Bhardwaj, B. Bhuyan, F. Bianchi, T. Bilka, S. Bilokin, D. Biswas, D. Bodrov, J. Borah, A. Bozek, M. Bračko, R. A. Briere, T. E. Browder, A. Budano, S. Bussino, M. Campajola, L. Cao, G. Casarosa, C. Cecchi, J. Cerasoli, M. -C. Chang, R. Cheaib, P. Cheema, V. Chekelian, B. G. Cheon, K. Chilikin, K. Chirapatpimol, H. -E. Cho, K. Cho, S. -J. Cho, S. -K. Choi, S. Choudhury, J. Cochran, L. Corona, S. Cunliffe, F. Dattola, E. De La Cruz-Burelo, S. A. De La Motte, G. De Nardo, G. De Pietro, R. de Sangro, M. Destefanis, R. Dhamija, F. Di Capua, J. Dingfelder, Z. Doležal, T. V. Dong, M. Dorigo, D. Dossett, S. Dreyer, S. Dubey, G. Dujany, P. Ecker, M. Eliachevitch, P. Feichtinger, T. Ferber, D. Ferlewicz, T. Fillinger, G. Finocchiaro, A. Fodor, F. Forti, A. Frey, B. G. Fulsom, A. Gabrielli, E. Ganiev, M. Garcia-Hernandez, G. Gaudino, V. Gaur, A. Gaz, A. Gellrich, G. Ghevondyan. 2023-01-19. A test of light-lepton universality in the rates of inclusive semileptonic $B$-meson decays at Belle II. https://doi.org/10.1103/physrevlett.131.051804

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