Observation of a Near-Threshold $D^0{\overline{D}}^0{\pi }^0$ Enhancement in $B\to D^0{\overline{D}}^0{\pi }^{0}K$ Decay

We report the first observation of a near-threshold enhancement in the $D^0{\overline{D}}^0{\pi }^0$ system from $B\to D^0{\overline{D}}^0{\pi }^{0}K$ decays using a $414{\mathrm{fb}}^{-1}$ data sample collected at the ${\rm Y}(4S)$ resonance. The enhancement peaks at a mass $M=3875.2\pm {0.7}_{-1.6}^{+0.3}\pm 0.8\mathrm{MeV}/c^2$ and the branching fraction for events in the peak is $\mathcal{B}(B\to D^0{\overline{D}}^0{\pi }^{0}K)=(1.22\pm 0.31\genfrac{}{}{0ex}{}{+0.23}{-0.30})\times {10}^{-4}$. The data were collected with the Belle detector at the KEKB energy-asymmetric $e^{+}{e}^{-}$ collider.