Measurement of the branching fraction and time-dependent $CP$ asymmetry for $B^0\to J/\psi {\pi }^0$ decays

Abstract

We measure the branching fraction and time-dependent $CP$-violating asymmetry for $B^0\to J/\psi {\pi }^0$ decays using a data sample of 711 $\mathrm{f}{\mathrm{b}}^{-1}$ collected on the ${\rm Y}(4S)$ resonance by the Belle experiment running at the KEKB $e^{+}{e}^{-}$ collider. The branching fraction is measured to be $\mathcal{B}(B^0\to J/\psi {\pi }^0)=[1.62\pm 0.11(\mathrm{stat})\pm 0.07(\mathrm{syst})]\times 10^{-5}$, which is the most precise measurement to date. The measured $CP$ asymmetry parameters are $\mathcal{S}=-0.59\pm 0.19(\mathrm{stat})\pm 0.03(\mathrm{syst})$ and $\mathcal{A}=-0.15\pm 0.14(\mathrm{stat}){}_{-0.03}^{+0.04}(\mathrm{syst})$. The mixing-induced $CP$ asymmetry ($\mathcal{S}$) differs from the case of no $CP$ violation by 3.0 standard deviations, and the direct $CP$ asymmetry ($\mathcal{A}$) is consistent with zero.

8 pages, 3 figures, submitted to Phys. Rev. D (RC)

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