Rare decays of B{yields}J/{psi}D{sup ()} and B{yields}{eta}{sub c}D{sup ()} in the perturbative QCD approach

Motivated by the recent measurement on the upper limit of B{sup 0}{yields}J/{psi}D branching ratio, we investigate the B{sup 0}{yields}J/{psi}D{sup (*)} and {eta}{sub c}D{sup (*)} decays in the framework of k{sub T} factorization. We find that these pure annihilation (W-exchange) decays possess branching ratios of the order 10{sup -5}{approx}10{sup -7}, which are just at the corner of being observable at the current running B factories. The measurements of these decay channels may help us to understand the QCD dynamics in the corresponding energy scale, and, especially, the distribution amplitudes of charmonium.