We have studied the color-suppressed hadronic decays of neutral B mesons into the final states $D^{(*)0}{\pi }^0$. Using $9.67\times {10}^6$ $B\overline{B}$ pairs collected with the CLEO detector, we observe the decays ${\overline{B}}^0\to D^0{\pi }^0$ and ${\overline{B}}^0\to D^{*0\mathrm{}}{\pi }^0$ with the branching fractions $B({\overline{B}}^0\to D^0{\pi }^0)=({2.74}_{-0.32\mathrm{}}^{+0.36\mathrm{}}\pm 0.55)\times {10}^{-4\mathrm{}}$ and $B({\overline{B}}^0\to D^{*0\mathrm{}}{\pi }^0)=({2.20}_{-0.52\mathrm{}}^{+0.59\mathrm{}}\pm 0.79)\times {10}^{-4\mathrm{}}$. The first error is statistical and the second systematic. The statistical significance of the $D^0{\pi }^0$ signal is $12.1\sigma$ ( $5.9\sigma$ for $D^{*0\mathrm{}}{\pi }^0$). Utilizing the ${\overline{B}}^0\to D^{(*)0}{\pi }^0$ branching fractions we determine the strong phases ${\delta }_{I,D(*)}$ between isospin $1/2$ and $3/2$ amplitudes in the $D\pi$ and $D^{*}\pi$ final states to be $\cos {\delta }_{I,D}=0.89\mathrm{}\pm 0.08$ and $\cos {\delta }_{I,D*}=0.89\mathrm{}\pm 0.08$, respectively.

• Received 22 October 2001

DOI:https://doi.org/10.1103/PhysRevLett.88.062001