Measurement of lepton mass squared moments in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>B</mml:mi><mml:mo stretchy="false">→</mml:mo><mml:msub><mml:mi>X</mml:mi><mml:mi>c</mml:mi></mml:msub><mml:mo>ℓ</mml:mo><mml:msub><mml:mover accent="true"><mml:mi>ν</mml:mi><mml:mo stretchy="false">¯</mml:mo></mml:mover><mml:mo>ℓ</mml:mo></mml:msub></mml:math> decays with the Belle II experiment
F. Abudinén, K. Adamczyk, L. Aggarwal, H. Ahmed, H. Aihara, Н. Акопов, A. Aloisio, N. Anh Ky, D. M. Asner, H. Atmacan, T. Aushev, V. Aushev, V. Babu, S. Bacher, H. Bae, S. Baehr, S. Bahinipati, P. Bambade, Sw. Banerjee, M. Barrett, J. Baudot, M. Bauer, A. Baur, Jürgen Becker, P. K. Behera, J. V. Bennett, F. U. Bernlochner, M. Bertemes, E. Bertholet, M. Bessner, S. Bettarini, B. Bhuyan, F. Bianchi, T. Bilka, D. Biswas, A. Bobrov, D. Bodrov, A. E. Bolz, J. Borah, A. Bożek, M. Bračko, P. Branchini, R. A. Briere, T. E. Browder, A. Budano, S. Bussino, M. Campajola, L. Cao, G. Casarosa, C. Cecchi, D. Červenkov, M.-C. Chang, P. Chang, R. Cheaib, P. Cheema, V. Chekelian, C. Chen, Y.-T. Chen, B. G. Cheon, K. Chilikin, K. Chirapatpimol, H.-E. Cho, K. Cho, S.-J. Cho, S.-K. Choi, S. Choudhury, D. Cinabro, L. Corona, L. Cremaldi, S. Cunliffe, T. Czank, F. Dattola, E. De La Cruz–Burelo, G. de Marino, G. De Nardo, M. De Nuccio, G. De Pietro, R. de Sangro, M. Destefanis, S. Dey, A. De Yta-Hernandez, R. Dhamija, A. Di Canto, F. Di Capua, J. Dingfelder, Z. Doležal, I. Domínguez Jiménez, T. V. Dong, M. Dorigo, K. Dort, D. Dossett, S. Dreyer, S. Dubey, S. Duell, G. Dujany, P. Ecker, M. Eliachevitch, D. Epifanov, P. Feichtinger, T. Ferber
Abstract
We present measurements of the first to fourth moments of the lepton mass squared ${q}^{2}$ of $B\ensuremath{\rightarrow}{X}_{c}\ensuremath{\ell}{\overline{\ensuremath{\nu}}}_{\ensuremath{\ell}}$ decays for $\ensuremath{\ell}=e$, $\ensuremath{\mu}$ and with ${X}_{c}$ a hadronic system containing a charm quark. These results use a sample of electron-positron collisions at the $\mathrm{\ensuremath{\Upsilon}}(4S)$ resonance corresponding to $62.8\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ of integrated luminosity and collected by the Belle II 2 experiment in 2019 and 2020. To identify the ${X}_{c}$ system and reconstruct ${q}^{2}$, one of the $B$ mesons from an $\mathrm{\ensuremath{\Upsilon}}(4S)\ensuremath{\rightarrow}B\overline{B}$ decay is fully reconstructed in a hadronic decay mode using a multivariate $B$ tagging algorithm. We report raw and central moments for ${q}^{2}>1.5\text{ }\text{ }{\mathrm{GeV}}^{2}/{c}^{4}$ up to ${q}^{2}>8.5\text{ }\text{ }{\mathrm{GeV}}^{2}/{c}^{4}$, probing up to 77% of the accessible $B\ensuremath{\rightarrow}{X}_{c}\ensuremath{\ell}{\overline{\ensuremath{\nu}}}_{\ensuremath{\ell}}$ phase space. This is the first measurement of moments in the experimentally challenging range of $[1.5,2.5]\text{ }\text{ }{\mathrm{GeV}}^{2}/{c}^{4}$. The results can be used for a new determination of $|{V}_{cb}|$ using inclusive $B\ensuremath{\rightarrow}{X}_{c}\ensuremath{\ell}{\overline{\ensuremath{\nu}}}_{\ensuremath{\ell}}$ decays.