Improved measurements of color-suppressed decays ${\overline{B}}^0\to D^0{\pi }^0$, $D^0\eta$, $D^0\omega$, $D^{*0}{\pi }^0$, $D^{*0}\eta$ and $D^{*0}\omega$

We present improved measurements of the branching fractions of the color-suppressed decays ${\overline{B}}^0\to D^{(*)0}{h}^0$, where $h^0$ represents a light neutral meson ${\pi }^0$, $\eta$ or $\omega$. The measurements are based on a data sample of $140{\mathrm{fb}}^{-1}$ collected at the ${\rm Y}(4S)$ resonance with the Belle detector at the KEKB energy-asymmetric $e^{+}{e}^{-}$ collider, corresponding to 7 times the luminosity of the previous Belle measurements. All the measured branching fractions fall in the range $1.4–2.4\times {10}^{-4}$, which is significantly higher than theoretical predictions based on naive factorization.

Figure 1

Tree level internal (a) and external (b) spectator diagrams for $\overline{B}\to D\pi$ decays.

Figure 2

Distributions of $M_{\mathrm{bc}}$ and $\Delta E$ for the decay modes ${\overline{B}}^0\to D^0{\pi }^0$ (a,b) and ${\overline{B}}^0\to D^{*0}{\pi }^0$ (c,d), with the three $D^0$ subdecay modes combined. The points represent the data, the solid lines show the result of the fit and the dash-dotted lines (peaking at $\Delta E\approx 0\mathrm{GeV}$ and $M_{\mathrm{bc}}\approx 5.28\mathrm{GeV}/c^2$) represent the signal contributions. The vertical dotted lines represent the signal region. For the $M_{\mathrm{bc}}$ distributions the upper long dashed line shows the continuumlike background contribution, with peaking background contribution represented by the lower long dashed line and cross-feed contribution represented by the bold dotted line. For the $\Delta E$ distributions, (b,d) the two long dashed curves show the $B$ background components (dominated by the color-allowed $B^{-}\to D^{(*)0}{\rho }^{-}$ modes) and the dotted line represents the continuum contribution and the bold dotted curve represents the cross-feed contribution.

Figure 3

Distributions of $M_{\mathrm{bc}}$ and $\Delta E$ for the decay modes ${\overline{B}}^0\to D^0\eta$ (a,b) and ${\overline{B}}^0\to D^{*0}\eta$ (c,d), with the three $D^0$ subdecay modes combined. For the $\Delta E$ distributions, (b) the long dashed curve represents the sum of $B$ background and continuum contributions; (d) the long dashed curve represents the $B$ background contribution with the dotted line representing the continuum contribution; in both (b,d) the bold dotted curves represent the cross-feed contributions. In (b) two bold dotted curves are visible, corresponding to cross-feed arising from $D^{*0}{h}^0$ final states; the broader distribution is the component with final states where $D^{*0}\to D^0\gamma$ and the other corresponds to final states where $D^{*0}\to D^0{\pi }^0$. Other conventions follow those described in the caption of Fig. 2.

Figure 4

Distributions of $M_{\mathrm{bc}}$ and $\Delta E$ for the decay modes ${\overline{B}}^0\to D^0\omega$ (a,b) and ${\overline{B}}^0\to D^{*0}\omega$ (c,d), with the three $D^0$ subdecay modes combined. The conventions follow those of Fig. 3.

Figure 5

Comparison of the measured branching fractions ($\times {10}^{-4}$) of the modes ${\overline{B}}^0\to D^{(*)0}{h}^0$, for each of the three $D^0$ subdecay modes and for the combined mode samples, as obtained from the $\Delta E$ fit, with the $M_{\mathrm{bc}}$ signal region requirement applied. The shaded band indicates the combined submode result. The BABAR results [5] from $M_{\mathrm{bc}}$ fits are also shown.