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

We present measurements of the branching fraction and time-dependent $CP$ asymmetries in $B^0\to J/\psi {\pi }^0$ decays based on $(231.8\pm 2.6)\times {10}^6{\rm Y}(4S)\to B\overline{B}$ decays collected with the BABAR detector at the SLAC PEP-II asymmetric-energy $B$ factory. We obtain a branching fraction $\mathcal{B}(B^0\to J/\psi {\pi }^0)=(1.94\pm 0.22(\mathrm{stat})\pm 0.17(\mathrm{syst}))\times {10}^{-5}$. We also measure the $CP$ asymmetry parameters $C=-0.21\pm 0.26(\mathrm{stat})\pm 0.06(\mathrm{syst})$ and $S=-0.68\pm 0.30(\mathrm{stat})\pm 0.04(\mathrm{syst})$.

Figure 1

Feynman diagrams of the color suppressed tree (top) and gluonic penguin (bottom) amplitudes contributing to the $B^0\to J/\psi {\pi }^0$ decay.

Figure 2

Signal enhanced distributions of $m_{\mathrm{ES}}$ (top), $\Delta E$ (center) and $\mathcal{F}$ (bottom) for the data (points). The solid line represents the total likelihood, the dashed line is the sum of the backgrounds and the dotted line is the signal. The undulations in the background model are the result of limited MC statistics available for defining the two-dimensional nonparametric PDFs.

Figure 3

The $\Delta t$ distribution for a sample of signal enhanced events tagged as $B^0$ (top) and ${\overline{B}}^0$ (middle). The dotted lines are the sum of backgrounds and the solid lines are the sum of signal and backgrounds. The time-dependent $CP$ asymmetry (see text) is also shown (bottom), where the curve is the measured asymmetry.