Penguin-dominated $B \to \phi K_1(1270)$ and $\phi K_1(1400)$ decays in   the perturbative QCD approach
  We investigate the CP-averaged branching ratios, the polarization fractions, the relative phases, and the CP-violating asymmetries of the penguin-dominated $B \to \phi K_1(1270) $ and $ \phi K_1(1400)$ decays in the perturbative QCD(pQCD) approach, where $K_1(1270)$ and $K_1(1400)$ are believed to be the mixtures of two distinct types of axial-vector $K_{1A}(^3P_1)$ and $K_{1B}(^1P_1)$ states with different behavior, however, their mixing angle $\theta_{K_1}$ is still a hot and controversial topic presently. By numerical evaluations with two different mixing angles $\theta_{K_1} \sim 33^\circ$ and $58^\circ$ and phenomenological analysis, we find that: (a) the pQCD predictions for the branching ratio, the longitudinal polarization fraction and the direct CP violation of $B^\pm \to \phi K_1(1270)^\pm$ decay with the smaller angle $33^\circ$ are in good agreement with the currently available data; (b) though the central values significantly exceed the available upper limit, both pQCD predictions of $Br(B^\pm \to \phi K_1(1400)^\pm)$ with two different mixing angles are consistent with that obtained in QCD factorization and with the preliminary data in 2$\sigma$ errors. These results and other relevant predictions for the considered decays will be further tested by the LHCb and the forthcoming Super-B experiments; (c) the weak annihilation contributions can play an important role in $B \to \phi K_1(1270)$ and $\phi K_1(1400)$ decays; (d) these pQCD predictions combined with the future precision measurements can examine the reliability of the factorization approach employed here, but also explore the complicated QCD dynamics and mixing angle $\theta_{K_1}$ of the axial-vector $K_1(1270)$ and $K_1(1400)$ system. 
Xin Liu, Zhi-Tian Zou and Zhen-Jun Xiao
hep-ph hep-ex