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arXiv · 2104.14871

First search for direct $CP$-violating asymmetry in $B^0 \to K^0 \pi^0$ decays at Belle II

Belle II Collaboration·F. Abudinén·I. Adachi·R. Adak·K. Adamczyk·P. Ahlburg·J. K. Ahn·H. Aihara·N. Akopov·A. Aloisio·F. Ameli·L. Andricek·N. Anh Ky·D. M. Asner·H. Atmacan·V. Aulchenko·T. Aushev·V. Aushev·T. Aziz·V. Babu·S. Bacher·S. Baehr·S. Bahinipati·A. M. Bakich·P. Bambade·Sw. Banerjee·S. Bansal·M. Barrett·G. Batignani·J. Baudot·A. Beaulieu·J. Becker·P. K. Behera·M. Bender·J. V. Bennett·E. Bernieri·F. U. Bernlochner·M. Bertemes·E. Bertholet·M. Bessner·S. Bettarini·V. Bhardwaj·B. Bhuyan·F. Bianchi·T. Bilka·S. Bilokin·D. Biswas·A. Bobrov·A. Bondar·G. Bonvicini·A. Bozek·M. Bračko·P. Branchini·N. Braun·R. A. Briere·T. E. Browder·D. N. Brown·A. Budano·L. Burmistrov·S. Bussino·M. Campajola·L. Cao·G. Caria·G. Casarosa·C. Cecchi·D. Červenkov·M. -C. Chang·P. Chang·R. Cheaib·V. Chekelian·C. Chen·Y. -C. Chen·Y. Q. 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. M. Cremaldi·D. Cuesta·S. Cunliffe·T. Czank·N. Dash·F. Dattola·E. De La Cruz-Burelo·G. de Marino·G. De Nardo·M. De Nuccio·G. De Pietro·R. de Sangro·B. Deschamps·M. Destefanis·S. Dey·A. De Yta-Hernandez
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Abstract

We report on the first measurement of the direct $CP$-violating asymmetry ($\mathcal{A}$) in the charmless decay $B^0 \to K^0\pi^0$ at Belle II and an updated measurement of its branching fraction ($\mathcal{B}$). We use a sample of electron-positron collisions collected in 2019 and 2020 at the $\Upsilon(4S)$ resonance and corresponding to $62.8$ $\text{fb}^{-1}$ of integrated luminosity. We reconstruct and select about $50$ $B^0 \to K_S^0 \pi^0$ candidates, and we measure $\mathcal{A}_{{K^0\pi^0}} = -0.40_{-0.44}^{+0.46} (\text{stat}) \pm 0.04 (\text{syst})$ and $\mathcal{B}(B^0 \to K^0 \pi^0) = [8.5_{-1.6}^{+1.7} (\text{stat}) \pm 1.2 (\text{syst})] \times 10^{-6}$. This is the first measurement of $CP$ violation in $B^0 \to K^0\pi^0$ decays reported by Belle II. The results agree with previous determinations and show a detector performance comparable with the best Belle results.

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Belle II Collaboration, F. Abudinén, I. Adachi, R. Adak, K. Adamczyk, P. Ahlburg, J. K. Ahn, H. Aihara, N. Akopov, A. Aloisio, F. Ameli, L. Andricek, N. Anh Ky, D. M. Asner, H. Atmacan, V. Aulchenko, T. Aushev, V. Aushev, T. Aziz, V. Babu, S. Bacher, S. Baehr, S. Bahinipati, A. M. Bakich, P. Bambade, Sw. Banerjee, S. Bansal, M. Barrett, G. Batignani, J. Baudot, A. Beaulieu, J. Becker, P. K. Behera, M. Bender, J. V. Bennett, E. Bernieri, F. U. Bernlochner, M. Bertemes, E. Bertholet, M. Bessner, S. Bettarini, V. Bhardwaj, B. Bhuyan, F. Bianchi, T. Bilka, S. Bilokin, D. Biswas, A. Bobrov, A. Bondar, G. Bonvicini, A. Bozek, M. Bračko, P. Branchini, N. Braun, R. A. Briere, T. E. Browder, D. N. Brown, A. Budano, L. Burmistrov, S. Bussino, M. Campajola, L. Cao, G. Caria, G. Casarosa, C. Cecchi, D. Červenkov, M. -C. Chang, P. Chang, R. Cheaib, V. Chekelian, C. Chen, Y. -C. Chen, Y. Q. 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. M. Cremaldi, D. Cuesta, S. Cunliffe, T. Czank, N. Dash, F. Dattola, E. De La Cruz-Burelo, G. de Marino, G. De Nardo, M. De Nuccio, G. De Pietro, R. de Sangro, B. Deschamps, M. Destefanis, S. Dey, A. De Yta-Hernandez. 2021-04-30. First search for direct $CP$-violating asymmetry in $B^0 \to K^0 \pi^0$ decays at Belle II. https://arxiv.org/abs/2104.14871

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