Fernando Abudinen ; Colm Murphy ; Takeo Higuchi

14 September 2021

Abstract: We report on new flavor-tagging algorithms developed to determine the quark-flavor content of bottom (B) mesons at Belle II. The algorithms provide essential inputs for measurements of quark-flavor mixing and charge-parity violation. We validate and evaluate the performance of the algorithms using hadronic B decays with flavor-specific final states reconstructed in a data set corresponding to an integrated luminosity of 62.8 fb$^{-1}$, collected at the Y(4S) resonance with the Belle II detector at the SuperKEKB collider. We measure the total effective tagging efficiency to be $\varepsilon_{\rm eff} = (30.0 \pm 1.2(stat) \pm 0.4(syst))\%$ for a category-based algorithm and $\varepsilon_{\rm eff} = (28.8 \pm 1.2(stat) \pm 0.4(syst))\%$ for a deep-learning-based algorithm.

Keyword(s): Flavor tagging, ; Bzero-AntiBzero mixing, ; CP violation, ; CKM angles, ; Multivariate analysis, ; Machine learning, ; Deep learning