Branching Ratio and CP Asymmetry of $B^0 \to \eta^{(\prime)}   \eta^{(\prime)}$ Decays in the Perturbative QCD Approach
  We calculate the CP averaged branching ratios and CP-violating asymmetries for $B^0 \to \eta \eta, \eta \eta^\prime$ and $\eta^\prime \eta^\prime$ decays by employing the perturbative QCD (pQCD) factorization approach. The pQCD predictions for the CP-averaged branching ratios are $Br(B^0 \to \eta \eta) \approx 0.67 \times 10^{-7}$, $Br(B^0 \to \eta \eta^\prime) \approx 0.18 \times 10^{-7}$, and $Br(B^0 \to \eta^{\prime} \eta^{\prime}) \approx 0.11 \times 10^{-7}$, which are consistent with currently available experimental upper limits. We also predict large CP-violating asymmetries for the considered three decay modes, which can be tested by the future B meson experiments. 
Zhen-jun Xiao, Dong-qin Guo and Xin-fen Chen