2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/182637Motivated by the recent measurement of the upper limit of ${B}^0 \to J/ψD$ branching ratio, which is important in accounting for the soft $J/ψ$ production in B decays, we investigate ${B}^0 \to J/ψD^{(\star)}$ and $η_c D^{(\star)}$ decays in perturbative QCD approach based on $k_T$ factorization. Being pure annihilation (W-exchange) decays, these branching ratios are estimated to be at the order of $10^{-5} \sim 10^{-7}$, which are just at the corner of being observable at the $B$ factories. The measurements of these decay channels may help us to understand the QCD dynamics in the corresponding energy scale, especially the reliability of pQCD approach to these processes.10 pages, 1 figureHigh Energy Physics - Phenomenologytext