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

We measure the branching fraction and time-dependent $CP$-violating asymmetry for $B^0\to J\mathrm{/}\psi {\pi }^0$ decays using a data sample of 711 $\mathrm{f}{\mathrm{b}}^{-1}$ collected on the $\mathrm{{\rm Y}}(4S)$ resonance by the Belle experiment running at the KEKB $e^{+}{e}^{-}$ collider. The branching fraction is measured to be $$\mathcal{B}$(B^0\to J/\psi\pi^0) = [1.62,\pm 0.11~({\rm stat}) \pm0.07~({\rm syst})]\times 10^{-5}$, which is the most precise measurement to date. The measured $CP$ asymmetry parameters are $$\mathcal{S}$ = -0.59,\pm 0.19~({\rm stat}) \pm 0.03~({\rm syst})$and$$\mathcal{A}$ = -0.15,\pm 0.14~({\rm stat}),^{+0.04}_{-0.03}~({\rm syst})$\mathrm{.}Themixing-induced$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.