New graph-neural-network flavor tagger for Belle II and measurement of $\sin 2{\varphi }_1$ in $B^0\to J/\psi K_{\text{S}}^0$ decays

Abstract

We present GFlaT, a new algorithm that uses a graph-neural-network to determine the flavor of neutral $B$ mesons produced in ${\rm Y}(4S)$ decays. It improves previous algorithms by using the information from all charged final-state particles and the relations between them. We evaluate its performance using $B$ decays to flavor-specific hadronic final states reconstructed in a 362 ${\text{fb}}^{-1}$ sample of electron-positron collisions collected at the ${\rm Y}(4S)$ resonance with the Belle II detector at the SuperKEKB collider. We achieve an effective tagging efficiency of $(37.40\pm 0.43\pm 0.36)\%$, where the first uncertainty is statistical and the second systematic, which is $18\%$ better than the previous Belle II algorithm. Demonstrating the algorithm, we use $B^0\to J/\psi K_{\text{S}}^0$ decays to measure the mixing-induced and direct $CP$ violation parameters, $S=(0.724\pm 0.035\pm 0.009)$ and $C=(-0.035\pm 0.026\pm 0.029)$.

15 pages, 9 figures

References in corpus (11)

• An Introduction to PYTHIA 8.2
• Measurement of CP Asymmetries and Branching Fractions in Charmless Two-Body B-Meson Decays to Pions and Kaons
• A Roadmap to Control Penguin Effects in $B_d^0\to J/\psi K_{\mathrm{S}}^0$ and $B_s^0\to J/\psi \varphi$
• The Design, Construction, Operation and Performance of the Belle II Silicon Vertex Detector
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• Observation of $CP$ violation in two-body $B_{(\mathrm{s})}^0$-meson decays to charged pions and kaons
• Measurement of CP violation in $B^0\to \psi (\to {\ell }^{+}{\ell }^{-})K_S^0(\to {\pi }^{+}{\pi }^{-})$ decays
• Penguin Effects in $B_d^0\to J/\psi K_S^0$ and $B_s^0\to J/\psi \varphi$
• CP violation and material interaction of neutral kaons in measurements of the CKM angle $\gamma$ using $B^{\pm }\to D{K}^{\pm }$ decays where $D\to K_{\text{S}}^0{\pi }^{+}{\pi }^{-}$
• Measurement of the $B^0$ lifetime and flavor-oscillation frequency using hadronic decays reconstructed in 2019-2021 Belle II data
• Measurement of decay-time-dependent $\text{CP}$ violation in $B^0\to J/\psi K_S^0$ decays using 2019-2021 Belle II data

Cited by in corpus (6)

• How to tame penguins: Advancing to high-precision measurements of ${\varphi }_d$ and ${\varphi }_s$
• Observation of the Singly Cabibbo-Suppressed Decay ${\Lambda }_c^{+}\to p{\pi }^0$
• Scalable Multi-Task Learning for Particle Collision Event Reconstruction with Heterogeneous Graph Neural Networks
• Observation of time-dependent $CP$ violation and measurement of the branching fraction of $B^0\to J/\psi {\pi }^0$ decays
• Unlocking time-dependent $CP$ violation without signal vertexing at $B$ factories
• Measurement of the branching fraction, polarization, and time-dependent $CP$ asymmetry in $B^0\to {\rho }^{+}{\rho }^{-}$ decays and constraint on the CKM angle ${\varphi }_2$