Observation of time-dependent $CP$ violation and measurement of the branching fraction of $B^0\to J/\psi {\pi }^0$ decays

Abstract

We present a measurement of the branching fraction and time-dependent charge-parity ($CP$) decay-rate asymmetries in $B^0\to J/\psi {\pi }^0$ decays. The data sample was collected with the Belle~II detector at the SuperKEKB asymmetric $e^{+}{e}^{-}$ collider in 2019-2022 and contains $(387\pm 6)\times 10^6$ $B\overline{B}$ meson pairs from ${\rm Y}(4S)$ decays. We reconstruct $392\pm 24$ signal decays and fit the $CP$ parameters from the distribution of the proper-decay-time difference of the two $B$ mesons. We measure the branching fraction to be $B(B^0\to J/\psi {\pi }^0)=(2.00\pm 0.12\pm 0.09)\times 10^{-5}$ and the direct and mixing-induced $CP$ asymmetries to be $C_{CP}=0.13\pm 0.12\pm 0.03$ and $S_{CP}=-0.88\pm 0.17\pm 0.03$, respectively, where the first uncertainties are statistical and the second are systematic. We observe mixing-induced $CP$ violation with a significance of $5.0$ standard deviations for the first time in this mode.

References in corpus (11)

• An Introduction to PYTHIA 8.2
• Averages of $b$-hadron, $c$-hadron, and $\tau$-lepton properties as of 2021
• Track Finding at Belle II
• The Design, Construction, Operation and Performance of the Belle II Silicon Vertex Detector
• In Pursuit of New Physics with $B_d^0\to J/\psi K^0$ and $B_s^0\to J/\psi \varphi$ Decays at the High-Precision Frontier
• Measurement of the integrated luminosity of data samples collected during 2019-2022 by the Belle II experiment
• Measurements of Beam Backgrounds in SuperKEKB Phase 2
• 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 $B_s^0\to J/\psi \varphi$
• 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
• Measurement of the Branching Fraction of $B^0\to J/\psi {\pi }^0$ Decays

Cited by in corpus (2)

• How to tame penguins: Advancing to high-precision measurements of ${\varphi }_d$ and ${\varphi }_s$
• Observation of $CP$ violation in $B^0\to J/\psi \rho (770{)}^0$ decays