Test of lepton flavor universality with a measurement of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>R</mml:mi><mml:mo stretchy="false">(</mml:mo><mml:msup><mml:mi>D</mml:mi><mml:mo>*</mml:mo></mml:msup><mml:mo stretchy="false">)</mml:mo></mml:math> using hadronic <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>B</mml:mi></mml:math> tagging at the Belle II experiment
I. Adachi, K. Adamczyk, L. Aggarwal, H. Ahmed, H. Aihara, Н. Акопов, A. Aloisio, N. Anh Ky, D. M. Asner, H. Atmacan, T. Aushev, V. Aushev, M. Aversano, R. Ayad, V. Babu, H. Bae, S. Bahinipati, P. Bambade, Sw. Banerjee, S. Bansal, M. Barrett, J. Baudot, M. Bauer, A. Baur, A. Beaubien, F. Becherer, Jürgen Becker, J. V. Bennett, F. U. Bernlochner, V. Bertacchi, M. Bertemes, E. Bertholet, M. Bessner, S. Bettarini, B. Bhuyan, F. Bianchi, L. Bierwirth, T. Bilka, S. Bilokin, D. Biswas, A. Bobrov, D. Bodrov, A. E. Bolz, A. Bondar, 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, J. Cerasoli, M.-C. Chang, P. Chang, R. Cheaib, P. Cheema, C. Chen, B. G. Cheon, K. Chilikin, K. Chirapatpimol, H.-E. Cho, K. Cho, S.-J. Cho, S.-K. Choi, S. Choudhury, J. Cochran, L. Corona, L. Cremaldi, S. Das, F. Dattola, E. De La Cruz–Burelo, S. A. De La Motte, 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, I. Domínguez Jiménez, 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
Abstract
The ratio of branching fractions <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:mi>R</a:mi><a:mo stretchy="false">(</a:mo><a:msup><a:mi>D</a:mi><a:mo>*</a:mo></a:msup><a:mo stretchy="false">)</a:mo><a:mo>=</a:mo><a:mi mathvariant="script">B</a:mi><a:mo stretchy="false">(</a:mo><a:mover accent="true"><a:mi>B</a:mi><a:mo stretchy="false">¯</a:mo></a:mover><a:mo stretchy="false">→</a:mo><a:msup><a:mi>D</a:mi><a:mo>*</a:mo></a:msup><a:msup><a:mi>τ</a:mi><a:mo>−</a:mo></a:msup><a:msub><a:mover accent="true"><a:mi>ν</a:mi><a:mo stretchy="false">¯</a:mo></a:mover><a:mi>τ</a:mi></a:msub><a:mo stretchy="false">)</a:mo><a:mo>/</a:mo><a:mi mathvariant="script">B</a:mi><a:mo stretchy="false">(</a:mo><a:mover accent="true"><a:mi>B</a:mi><a:mo stretchy="false">¯</a:mo></a:mover><a:mo stretchy="false">→</a:mo><a:msup><a:mi>D</a:mi><a:mo>*</a:mo></a:msup><a:msup><a:mo>ℓ</a:mo><a:mo>−</a:mo></a:msup><a:msub><a:mover accent="true"><a:mi>ν</a:mi><a:mo stretchy="false">¯</a:mo></a:mover><a:mo>ℓ</a:mo></a:msub><a:mo stretchy="false">)</a:mo></a:math>, where <u:math xmlns:u="http://www.w3.org/1998/Math/MathML" display="inline"><u:mo>ℓ</u:mo></u:math> is an electron or muon, is measured using a Belle II data sample with an integrated luminosity of <w:math xmlns:w="http://www.w3.org/1998/Math/MathML" display="inline"><w:mn>189</w:mn><w:mtext> </w:mtext><w:mtext> </w:mtext><w:msup><w:mi>fb</w:mi><w:mrow><w:mo>−</w:mo><w:mn>1</w:mn></w:mrow></w:msup></w:math> at the SuperKEKB asymmetric-energy <y:math xmlns:y="http://www.w3.org/1998/Math/MathML" display="inline"><y:msup><y:mi>e</y:mi><y:mo>+</y:mo></y:msup><y:msup><y:mi>e</y:mi><y:mo>−</y:mo></y:msup></y:math> collider. Data is collected at the <ab:math xmlns:ab="http://www.w3.org/1998/Math/MathML" display="inline"><ab:mi mathvariant="normal">ϒ</ab:mi><ab:mo stretchy="false">(</ab:mo><ab:mrow><ab:mn>4</ab:mn><ab:mi mathvariant="normal">S</ab:mi></ab:mrow><ab:mo stretchy="false">)</ab:mo></ab:math> resonance, and one <gb:math xmlns:gb="http://www.w3.org/1998/Math/MathML" display="inline"><gb:mi>B</gb:mi></gb:math> meson in the <ib:math xmlns:ib="http://www.w3.org/1998/Math/MathML" display="inline"><ib:mi mathvariant="normal">ϒ</ib:mi><ib:mo stretchy="false">(</ib:mo><ib:mrow><ib:mn>4</ib:mn><ib:mi mathvariant="normal">S</ib:mi></ib:mrow><ib:mo stretchy="false">)</ib:mo><ib:mo stretchy="false">→</ib:mo><ib:mi>B</ib:mi><ib:mover accent="true"><ib:mi>B</ib:mi><ib:mo stretchy="false">¯</ib:mo></ib:mover></ib:math> decay is fully reconstructed in hadronic decay modes. The accompanying signal <rb:math xmlns:rb="http://www.w3.org/1998/Math/MathML" display="inline"><rb:mi>B</rb:mi></rb:math> meson is reconstructed as <tb:math xmlns:tb="http://www.w3.org/1998/Math/MathML" display="inline"><tb:mover accent="true"><tb:mi>B</tb:mi><tb:mo stretchy="false">¯</tb:mo></tb:mover><tb:mo stretchy="false">→</tb:mo><tb:msup><tb:mi>D</tb:mi><tb:mo>*</tb:mo></tb:msup><tb:msup><tb:mi>τ</tb:mi><tb:mo>−</tb:mo></tb:msup><tb:msub><tb:mover accent="true"><tb:mi>ν</tb:mi><tb:mo stretchy="false">¯</tb:mo></tb:mover><tb:mi>τ</tb:mi></tb:msub></tb:math> using leptonic <ac:math xmlns:ac="http://www.w3.org/1998/Math/MathML" display="inline"><ac:mi>τ</ac:mi></ac:math> decays. The normalization decay, <cc:math xmlns:cc="http://www.w3.org/1998/Math/MathML" display="inline"><cc:mover accent="true"><cc:mi>B</cc:mi><cc:mo stretchy="false">¯</cc:mo></cc:mover><cc:mo stretchy="false">→</cc:mo><cc:msup><cc:mi>D</cc:mi><cc:mo>*</cc:mo></cc:msup><cc:msup><cc:mo>ℓ</cc:mo><cc:mo>−</cc:mo></cc:msup><cc:msub><cc:mover accent="true"><cc:mi>ν</cc:mi><cc:mo stretchy="false">¯</cc:mo></cc:mover><cc:mo>ℓ</cc:mo></cc:msub></cc:math>, produces the same observable final-state particles. The ratio of branching fractions is extracted in a simultaneous fit to two signal-discriminating variables in both channels and yields <jc:math xmlns:jc="http://www.w3.org/1998/Math/MathML" display="inline"><jc:mi>R</jc:mi><jc:mo stretchy="false">(</jc:mo><jc:msup><jc:mi>D</jc:mi><jc:mo>*</jc:mo></jc:msup><jc:mo stretchy="false">)</jc:mo><jc:mo>=</jc:mo><jc:msubsup><jc:mn>0.262</jc:mn><jc:mrow><jc:mo>−</jc:mo><jc:mn>0.039</jc:mn></jc:mrow><jc:mrow><jc:mo>+</jc:mo><jc:mn>0.041</jc:mn></jc:mrow></jc:msubsup><jc:mo stretchy="false">(</jc:mo><jc:mrow><jc:mi>stat</jc:mi></jc:mrow><jc:msubsup><jc:mo stretchy="false">)</jc:mo><jc:mrow><jc:mo>−</jc:mo><jc:mn>0.032</jc:mn></jc:mrow><jc:mrow><jc:mo>+</jc:mo><jc:mn>0.035</jc:mn></jc:mrow></jc:msubsup><jc:mo stretchy="false">(</jc:mo><jc:mrow><jc:mi>syst</jc:mi></jc:mrow><jc:mo stretchy="false">)</jc:mo></jc:math>. This result is consistent with the current world average and with Standard Model predictions. Published by the American Physical Society 2024