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arXiv · 2505.02912

Measurement of the time-integrated $CP$ asymmetry in $D^0\to\pi^0\pi^0$ decays at Belle II

Belle II Collaboration·I. Adachi·Y. Ahn·N. Akopov·S. Alghamdi·M. Alhakami·A. Aloisio·N. Althubiti·K. Amos·M. Angelsmark·N. Anh Ky·C. Antonioli·D. M. Asner·H. Atmacan·T. Aushev·M. Aversano·R. Ayad·V. Babu·H. Bae·N. K. Baghel·S. Bahinipati·P. Bambade·Sw. Banerjee·M. Barrett·M. Bartl·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·D. Biswas·A. Bobrov·D. Bodrov·A. Bondar·J. Borah·A. Boschetti·A. Bozek·M. Bračko·P. Branchini·R. A. Briere·T. E. Browder·A. Budano·S. Bussino·M. Campajola·L. Cao·G. Casarosa·C. Cecchi·P. Cheema·B. G. Cheon·K. Chilikin·J. Chin·K. Chirapatpimol·H. -E. Cho·K. Cho·S. -J. Cho·S. -K. Choi·S. Choudhury·I. Consigny·L. Corona·J. X. Cui·E. De La Cruz-Burelo·S. A. De La Motte·G. De Pietro·R. de Sangro·M. Destefanis·A. Di Canto·J. Dingfelder·Z. Doležal·I. Domínguez Jiménez·T. V. Dong·M. Dorigo·G. Dujany·P. Ecker·D. Epifanov·J. Eppelt·R. Farkas·P. Feichtinger·T. Ferber·T. Fillinger·C. Finck·G. Finocchiaro·A. Fodor·F. Forti·B. G. Fulsom·A. Gabrielli·A. Gale·E. Ganiev·M. Garcia-Hernandez·R. Garg·G. Gaudino
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Abstract

We measure the time-integrated $CP$ asymmetry, $A_{CP}$, in $D^0\to\pi^0\pi^0$ decays reconstructed in $e^+e^-\to c\bar{c}$ events collected by Belle II during 2019--2022. The data corresponds to an integrated luminosity of 428$\mathrm{fb}^{-1}$. The $D^0$ decays are required to originate from the flavor-conserving $D^{*+} \to D^0 \pi^+$ decay to determine the charm flavor at production time. Control samples of $D^0\to K^- \pi^+$ decays, with or without an associated pion from a $D^{*+}$ decay, are used to correct for detection asymmetries. The result, $A_{CP}(D^0\to\pi^0\pi^0) = (0.30\pm 0.72\pm 0.20)\%$, where the first uncertainty is statistical and the second systematic, is consistent with $CP$ symmetry.

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Belle II Collaboration, I. Adachi, Y. Ahn, N. Akopov, S. Alghamdi, M. Alhakami, A. Aloisio, N. Althubiti, K. Amos, M. Angelsmark, N. Anh Ky, C. Antonioli, D. M. Asner, H. Atmacan, T. Aushev, M. Aversano, R. Ayad, V. Babu, H. Bae, N. K. Baghel, S. Bahinipati, P. Bambade, Sw. Banerjee, M. Barrett, M. Bartl, 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, D. Biswas, A. Bobrov, D. Bodrov, A. Bondar, J. Borah, A. Boschetti, A. Bozek, M. Bračko, P. Branchini, R. A. Briere, T. E. Browder, A. Budano, S. Bussino, M. Campajola, L. Cao, G. Casarosa, C. Cecchi, P. Cheema, B. G. Cheon, K. Chilikin, J. Chin, K. Chirapatpimol, H. -E. Cho, K. Cho, S. -J. Cho, S. -K. Choi, S. Choudhury, I. Consigny, L. Corona, J. X. Cui, E. De La Cruz-Burelo, S. A. De La Motte, G. De Pietro, R. de Sangro, M. Destefanis, A. Di Canto, J. Dingfelder, Z. Doležal, I. Domínguez Jiménez, T. V. Dong, M. Dorigo, G. Dujany, P. Ecker, D. Epifanov, J. Eppelt, R. Farkas, P. Feichtinger, T. Ferber, T. Fillinger, C. Finck, G. Finocchiaro, A. Fodor, F. Forti, B. G. Fulsom, A. Gabrielli, A. Gale, E. Ganiev, M. Garcia-Hernandez, R. Garg, G. Gaudino. 2025-05-05. Measurement of the time-integrated $CP$ asymmetry in $D^0\to\pi^0\pi^0$ decays at Belle II. https://doi.org/10.1103/vg9c-xvdc

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