Implications of Recent ${\bar{B}}^0\to D^{(\ast )0}{X}^0$ Measurements

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: $\mathrm{\mid }{a}_2(D\pi )\mathrm{\mid }=0.40-0.55$ and $\mathrm{\mid }{a}_2(D^{\ast }\pi )\mathrm{\mid }=0.25-0.35$ 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, $a_2^{eff}\mathrm{/}{a}_1^{eff}$ and $a_2^{eff}$ will become smaller. The large value of $\mathrm{\mid }{a}_2(D\pi )\mathrm{\mid }$ compared to $\mathrm{\mid }{a}_2^{eff}(D\pi )\mathrm{\mid }$ 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.