Oskar Tittel

06 November 2023

Abstract: We report on new time-dependent \CP violation measurements using the full dataset of \belletwo collected between 2019-2022 and on improved analysis software. Hadronic penguin decays, which proceed via a $b \to \qqbar s$ transition, are loop dominated, and thus sensitive to new physics. in this class, we measure the time-dependent \CP violation parameters $\ccp = -0.19 \pm 0.08 \pm 0.03$ and $\scp = 0.67 \pm 0.10 \pm 0.04$ in the decay $\Bz \to \eta' K_{S}^{0}$. 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 $\ccp = 0.10 \pm 0.13 \pm 0.03$ and $\scp = 0.00 \pm 0.27 \pm 0.04$ in exclusive decays to $\Bz \to K^{*0} \gamma$ and $\ccp = -0.06 \pm 0.25 \pm 0.07$ and $\scp = 0.04 \pm 0.45 \pm 0.10$ in inclusive $\Bz \to K_{S}^{0} \pi^{0} \gamma$ 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 \belletwo. The increased effective tagging efficiency of $\epsilon_{tag} = (37.40 \pm 0.43 \pm 0.34)\%$ is validated on the channel $\Bz \to J/\psi K_{S}^{0}$. The measured values are $\ccp = -0.035 \pm 0.026 \pm 0.012$ and $\scp = 0.724 \pm 0.035 \pm 0.014$