Study of W-exchange Mode $D^0 \to \phi \bar K^0$
  We calculate the branching ratio of $D^0 \to \phi \bar K^0$ decay using the so-called perturbation QCD approach based on $k_T$ factorization. Our result shows this branching ratio is $(8.7 \pm1.4)\times 10^{-3}$, which is consistent with experimental data. We hope the CLEO-C and BES-III can measure it more accurately, which will help us to understand QCD dynamics and $D$ meson weak decays. 
Dong-Sheng Du, Ying Li, Cai-Dian L\"u