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Conference Paper

Recent time-dependent measurements of CP violation at Belle II


Tittel,  Oskar P.
Max Planck Institute for Physics, Max Planck Society and Cooperation Partners;

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Tittel, O. P. (2023). Recent time-dependent measurements of CP violation at Belle II. Proceedings of Science, 449, 345.

Cite as: https://hdl.handle.net/21.11116/0000-000F-1174-B
We report on new time-dependent CP violation measurements using the full dataset of Belle II collected between 2019-2022 and on improved analysis software. Hadronic penguin decays, which proceed via a b to q q-bar s transition, are loop dominated, and thus sensitive to new physics. in this class, we measure the time-dependent CP violation parameters C_CP = -0.19 ± 0.08 ± 0.03 and S_CP = 0.67 ± 0.10 ± 0.04 in the decay B0 to eta' K0_S. In b to gamma(s,d) transitions, radiative penguin decays, the mixing-induced CP violation is suppressed by the polarization of the photon. New physics contributions could, however, lead to a sizable mixing-induced term. Here, we measure C_CP = 0.10 ± 0.13 ± 0.03 and S_CP = 0.00 ± 0.27 ± 0.04 in exclusive decays to B0 to K*0 gamma and C_CP = -0.06 ± 0.25 ± 0.07 and S_CP = 0.04 ± 0.45 ± 0.10 in inclusive B0 to K0_S pi0 gamma decays excluding a K*0 mass-region. These measurements require a flavor tagging algorithm. A flavor tagger based on a graph neural network was developed at Belle II. The increased effective tagging efficiency of epsilon_tag = (37.40 ± 0.43 ± 0.34)% is validated on the channel B0 to J/psi K0_S. The measured values are C_CP = -0.035 ± 0.026 ± 0.012 and S_CP = 0.724 ± 0.035 ± 0.014.