Study of B_(c)to J/psi K decays in the perturbative QCD approach

In this note, we calculate the branching ratio of B_c\to J/\psi K in the framework of perturbative QCD approach based on k_T factorization. This decay can occur only via tree level diagrams in the Standard Model. We find that the branching ratio of B_c\to J/\psi K is about (1-3)\times10^{-4}. The large branching ratio and the clear signals of the final states make the measurement of B_c\to J/\psi K easily at LHC-b experiments.