New graph-neural-network flavor tagger for Belle II and measurement of sin <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mn>2</mml:mn><mml:msub><mml:mi>ϕ</mml:mi><mml:mn>1</mml:mn></mml:msub></mml:math> in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msup><mml:mi>B</mml:mi><mml:mn>0</mml:mn></mml:msup><mml:mo stretchy="false">→</mml:mo><mml:mi>J</mml:mi><mml:mo>/</mml:mo><mml:mi>ψ</mml:mi><mml:msubsup><mml:mi>K</mml:mi><mml:mi mathvariant="normal">S</mml:mi><mml:mn>0</mml:mn></mml:msubsup></mml:math> decays
I. Adachi, 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, 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, L. Bierwirth, T. Bilka, S. Bilokin, D. Biswas, A. Bobrov, D. Bodrov, A. E. Bolz, A. Bondar, 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, P. Cheema, C. Chen, B. G. Cheon, K. Chilikin, K. Chirapatpimol, H.-E. Cho, K. Cho, S.-J. Cho, S. -J. Cho, S. Choudhury, J. Cochran, L. Corona, 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, S. Dey, R. Dhamija, A. Di Canto, F. Di Capua, Z. Doležal, T. V. Dong, M. Dorigo, K. Dort, D. Dossett, S. Dreyer, S. Dubey, G. Dujany, P. Ecker, M. Eliachevitch, P. Feichtinger, T. Ferber, D. Ferlewicz, T. Fillinger, C. Finck, G. Finocchiaro, A. Fodor, F. Forti, A. Frey
Abstract
We present GFlaT, a new algorithm that uses a graph-neural-network to determine the flavor of neutral <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:mi>B</a:mi></a:math> mesons produced in <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"><c:mi mathvariant="normal">ϒ</c:mi><c:mo stretchy="false">(</c:mo><c:mn>4</c:mn><c:mi>S</c:mi><c:mo stretchy="false">)</c:mo></c:math> decays. It improves previous algorithms by using the information from all charged final-state particles and the relations between them. We evaluate its performance using <h:math xmlns:h="http://www.w3.org/1998/Math/MathML" display="inline"><h:mi>B</h:mi></h:math> decays to flavor-specific hadronic final states reconstructed in a <j:math xmlns:j="http://www.w3.org/1998/Math/MathML" display="inline"><j:mn>362</j:mn><j:mtext> </j:mtext><j:mtext> </j:mtext><j:msup><j:mi>fb</j:mi><j:mrow><j:mo>−</j:mo><j:mn>1</j:mn></j:mrow></j:msup></j:math> sample of electron-positron collisions collected at the <l:math xmlns:l="http://www.w3.org/1998/Math/MathML" display="inline"><l:mi mathvariant="normal">ϒ</l:mi><l:mo stretchy="false">(</l:mo><l:mn>4</l:mn><l:mi>S</l:mi><l:mo stretchy="false">)</l:mo></l:math> resonance with the Belle II detector at the SuperKEKB collider. We achieve an effective tagging efficiency of <q:math xmlns:q="http://www.w3.org/1998/Math/MathML" display="inline"><q:mo stretchy="false">(</q:mo><q:mn>37.40</q:mn><q:mo>±</q:mo><q:mn>0.43</q:mn><q:mo>±</q:mo><q:mn>0.36</q:mn><q:mo>%</q:mo><q:mo stretchy="false">)</q:mo></q:math>, where the first uncertainty is statistical and the second systematic, which is 18% better than the previous Belle II algorithm. Demonstrating the algorithm, we use <u:math xmlns:u="http://www.w3.org/1998/Math/MathML" display="inline"><u:msup><u:mi>B</u:mi><u:mn>0</u:mn></u:msup><u:mo stretchy="false">→</u:mo><u:mrow><u:mi>J</u:mi><u:mo>/</u:mo><u:mi>ψ</u:mi></u:mrow><u:msubsup><u:mi>K</u:mi><u:mi mathvariant="normal">S</u:mi><u:mn>0</u:mn></u:msubsup></u:math> decays to measure the mixing-induced and direct <y:math xmlns:y="http://www.w3.org/1998/Math/MathML" display="inline"><y:mi>C</y:mi><y:mi>P</y:mi></y:math> violation parameters, <ab:math xmlns:ab="http://www.w3.org/1998/Math/MathML" display="inline"><ab:mi>S</ab:mi><ab:mo>=</ab:mo><ab:mo stretchy="false">(</ab:mo><ab:mn>0.724</ab:mn><ab:mo>±</ab:mo><ab:mn>0.035</ab:mn><ab:mo>±</ab:mo><ab:mn>0.009</ab:mn><ab:mo stretchy="false">)</ab:mo></ab:math> and <eb:math xmlns:eb="http://www.w3.org/1998/Math/MathML" display="inline"><eb:mi>C</eb:mi><eb:mo>=</eb:mo><eb:mo stretchy="false">(</eb:mo><eb:mo>−</eb:mo><eb:mn>0.035</eb:mn><eb:mo>±</eb:mo><eb:mn>0.026</eb:mn><eb:mo>±</eb:mo><eb:mn>0.029</eb:mn><eb:mo stretchy="false">)</eb:mo></eb:math>. Published by the American Physical Society 2024