Revisiting $B\to K^*\pi$ and $B\to K\rho$ decays using the modified perturbative QCD approach

We revisit $B\to K^*\pi$ and $B\to K\rho$ decay processes using the modified perturbative QCD approach, which is developed based on the perturbative QCD approach with a few improvements. A critical infrared cutoff scale $\mu_c$ is introduced to separate hard and soft contributions in the decay process. Hard contributions with scale $\mu$ larger than $\mu_c$ are calculated with perturbative QCD, and soft contributions with $\mu<\mu_c$ are described in terms of soft transition and production form factors. In addition, color-octet contributions are considered phenomenologically. The branching fractions and $CP$ violations of $B\to K^*\pi$, $K\rho$ decays are calculated. With appropriate parameter inputs, the theoretical results can be in good agreement with experimental data.