We present a measurement of the branching fraction for the Cabibbo- and color-suppressed $B^0\to {\chi }_{c1}{\pi }^0$ decay based on a data sample of $657\times {10}^{6}B\overline{B}$ events collected at the ${\rm Y}(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^{+}{e}^{-}$ collider. We observe a signal of $40\pm 9$ events with a significance of $4.7\sigma$ including systematic uncertainties. The measured branching fraction is $\mathcal{B}(B^0\to {\chi }_{c1}{\pi }^0)=(1.12\pm 0.25(\mathrm{stat})\pm 0.12(\mathrm{syst}.))\times {10}^{-5}$.

• Received 11 September 2008

DOI:https://doi.org/10.1103/PhysRevD.78.091104