Non-factorizable effects on $\Bbar^0\to D^{(*)0}\pi^0$

Non-factorizable effects on the color-suppressed $B\to D^{(*)}\pi$ decay modes are analyzed. Recent observations of $\Bbar^0\to D^{(*)0}\pi^0$ by Belle and CLEO strongly suggest that there exists a non-zero strong phase difference between color-allowed and color-suppressed decay modes, and the factorization parameter $a_2$ associated with the color-suppressed decay mode is process dependent. In the heavy quark limit where $b$ and $c$ are heavy, the process dependence of $a_2(D\pi,D^*\pi)$ is due to the different configuration of the heavy quark spin relative to the light degrees of freedom. From the experimental data, the heavy quark spin symmetry breaking contributions to the non-fatorizable effects are estimated to be $23-28$.