  The recent measurements of the color-suppressed modes $\bar B^0\to
D^{(*)0}\pi^0$ imply non-vanishing relative final-state interaction (FSI)
phases among various $\bar B\to D\pi$ decay amplitudes. Depending on whether or
not FSIs are implemented in the topological quark-diagram amplitudes, two
solutions for the parameters $a_1$ and $a_2$ are extracted from data using
various form-factor models. It is found that $a_2$ is not universal:
$|a_2(D\pi)|= 0.40-0.55$ and $|a_2(D^*\pi)|= 0.25-0.35$ with a relative phase
of order $(50-55)^\circ$ between $a_1$ and $a_2$. If FSIs are not included in
quark-diagram amplitudes from the outset, $a_2^{eff}/a_1^{eff}$ and $a_2^{eff}$
will become smaller. The large value of $|a_2(D\pi)|$ compared to
$|a_2^{eff}(D\pi)|$ or naive expectation implies the importance of
long-distance FSI contributions to color-suppressed internal $W$-emission via
final-state rescatterings of the color-allowed tree amplitude.

High Energy Physics - Phenomenology;High Energy Physics - Experiment