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.

Figure 1

(a) Scatter plot of $\Delta E$ and $M_{D^0{\overline{D}}^0{\pi }^0}$ distribution in the data sample. (b)–(m) $\Delta E$ distributions in $8\mathrm{MeV}/c^2$ $D^0{\overline{D}}^0{\pi }^0$ mass bins for a possible $B\to D^0{\overline{D}}^0{\pi }^{0}K$ signal in data.

Figure 2

Projection of the unbinned fit (a) $Q$ value ($=M_{D^0{\overline{D}}^0{\pi }^0}-2M_{D^0}-M_{{\pi }^0}$) in $\Delta E$ signal region ($|\Delta E|<25\mathrm{MeV}$) and (b) $\Delta E$ in the signal region of $Q$ value ($6\mathrm{MeV}/c^2$ $<Q$ value $<14\mathrm{MeV}/c^2$). The dots are data points, the hatched histogram corresponds to combinatorial background; the dashed line indicates the total background and the solid line is from the combined fitting function.