Evidence forCPViolation inB0→J/ψπ0Decays

We present measurements of the branching fraction and time-dependent $CP$ asymmetries in $B^0\to J/\psi {\pi }^0$ decays based on $466\times {10}^6$ ${\rm Y}(4S)\to B\overline{B}$ events collected with the BABAR detector at the SLAC PEP-II asymmetric-energy $B$ factory. We measure the $CP$ asymmetry parameters $S=-1.23\pm 0.21(\mathrm{stat})\pm 0.04(\mathrm{syst})$ and $C=-0.20\pm 0.19(\mathrm{stat})\pm 0.03(\mathrm{syst})$, where the measured value of ($S$, $C$) is 4.0 standard deviations from (0, 0) including systematic uncertainties. The branching fraction is determined to be $\mathcal{B}(B^0\to J/\psi {\pi }^0)=[1.69\pm 0.14(\mathrm{stat})\pm 0.07(\mathrm{syst})]\times {10}^{-5}$.