Mass distribution of $\pi ^0$ candidates shown with the fit projection for the (left) signal and (right) normalisation modes. The dashed line and coloured regions represent the $\pi ^0$ produced at the interaction region (IR) and the other fit components, respectively.

Mass distribution of $ B $ candidates shown with the fit projection for (left) signal and (right) normalisation modes. The dashed line and coloured regions represent $ B ^0 \rightarrow { J \mskip -3mu/\mskip -2mu\psi } \pi ^0 $ or $ B ^+ \rightarrow { J \mskip -3mu/\mskip -2mu\psi } K ^{*+} $ decays and different sources of background, respectively.

Mass distribution of $ { J \mskip -3mu/\mskip -2mu\psi }$ $\rho ^+$ candidates shown with the fit projection in the (left) $ B ^+$ and (right) $ B _ c ^+$ signal region. In the latter case, the selection requirements are relaxed to accommodate the small production of $ B _ c ^+$ mesons. The dashed line and coloured regions represent $ B ^+$ or $ B _ c ^+$ decays to the $ { J \mskip -3mu/\mskip -2mu\psi }$ $\rho ^+$ final-state and different sources of background, respectively.

Mass distribution of (left) $ { J \mskip -3mu/\mskip -2mu\psi }$ $\pi ^+$ and (right) $ { J \mskip -3mu/\mskip -2mu\psi }$ $ K ^{*0}$ candidates shown with the fit projection. The dashed lines and coloured regions represent $ B ^+ \rightarrow { J \mskip -3mu/\mskip -2mu\psi } \pi ^+ $ or $ B _{( s )}^0 \rightarrow { J \mskip -3mu/\mskip -2mu\psi } K ^{*0} $ decays and different sources of background, respectively.

Branching fraction for $ B ^0 \rightarrow { J \mskip -3mu/\mskip -2mu\psi } \pi ^0 $ decays as measured in this analysis and by the BaBar and Belle collaborations. The world average and its uncertainty (PDG 2022) are indicated by the solid and dashed lines, respectively, representing a combination of the Belle , BaBar and CLEO measurements [10,11,47]. The latter measurement is affected by a much larger error and is not shown.

Animated gif made out of all figures.

Results of the fit to the $ { J \mskip -3mu/\mskip -2mu\psi }$ $\pi ^0$ mass: the yields of signal and background decays, the yield of genuine $\pi ^0$ combinatorial candidates ($N_{\rm B}$), the ratio between the signal width in data and in simulation ($R_{\sigma}$), and the shape parameter of the combinatorial background ($\alpha_{\rm B}$).

Results of the fit to the $ { J \mskip -3mu/\mskip -2mu\psi }$ $ K ^+$ $\pi ^0$ mass: the yields of normalisation and partially reconstructed background decays, the yield of combinatorial candidates ($N_{\textrm{B}, K ^* }$), the ratio between the normalisation width in data and in simulation ($R_{\sigma, K ^* }$), the difference between the normalisation mean in data and in simulation ($D_{\mu, K ^* }$), the difference $D_{\mu, K ^* \pi}$ for partially reconstructed decays and the shape parameter of the combinatorial background ($\alpha_{\textrm{B}, K ^* }$).

Summary of uncertainties on the ratio of branching fractions for $ B ^0 \rightarrow { J \mskip -3mu/\mskip -2mu\psi } \pi ^0 $ and $ B ^+ \rightarrow { J \mskip -3mu/\mskip -2mu\psi } K ^{*+} $ decays. Systematic uncertainties of individual sources are added in quadrature.