Soft Gluon Suppression of $1\mathrm{/}{N}_c$ Contributions in Color Suppressed Heavy Meson Decays

We discuss the non-factorizable terms in color suppressed (Class II) decays. Our emphasis is on the non-perturbative soft gluon exchange mechanism, which has been previously found to be responsible for the rule of discarding $1\mathrm{/}{N}_c$ in the Class I decays. The non-factorizable contribution to the decays ${\bar{B}}^0\to D^0{\pi }^0$ at the tree level is estimated within the light cone QCD sum rule method which combines the technique of the QCD sum rules with the description of the pion in terms of the set of wave functions of increasing twist. We find that the same soft gluon exchange mechanism tends to cancel the $1\mathrm{/}{N}_c$ term in the factorized amplitude.