Nonfactorizable contributions to $B to D^{(*)} M$ decays

While the factorization assumption works well for many two-body nonleptonic $B$ meson decay modes, the recent measurement of $bar Bto D^{(*)0}M^0$ with $M=pi$, $rho$ and $omega$ shows large deviation from this assumption. We analyze the $Bto D^{(*)}M$ decays in the perturbative QCD approach based on $k_T$ factorization theorem, in which both factorizable and nonfactorizable contributions can be calculated in the same framework. Our predictions for the Bauer-Stech-Wirbel parameters, $|a_2/a_1|= 0.43pm 0.04$ and $Arg(a_2/a_1)sim -42^circ$ and $|a_2/a_1|= 0.47pm 0.05$ and $Arg(a_2/a_1)sim -41^circ$, are consistent with the observed $Bto Dpi$ and $Bto D^*pi$ branching ratios, respectively. It is found that the large magnitude $|a_2|$ and the large relative phase between $a_2$ and $a_1$ come from color-suppressed nonfactorizable amplitudes. Our predictions for the ${bar B}^0to D^{(*)0}rho^0$, $D^{(*)0}omega$ branching ratios can be confronted with future experimental data.