Rare decays ofB→J/ψD(*)andB→ηcD(*)in the perturbative QCD approach

Motivated by the recent measurement on the upper limit of B-0 -> J/psi D branching ratio, we investigate the B-0 -> J/psi D-(star) and eta D-c((star)) decays in the framework of k(T) factorization. We find that these pure annihilation (W-exchange) decays possess branching ratios of the order 10(-5)similar to 10(-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.