Branching ratio and CP asymmetry of B→πη(′) decays in the perturbative QCD approach

We calculate the branching ratios and CP-violating asymmetries for B0→π0η(′) and B+→π+η(′) decays in the perturbative QCD (pQCD) factorization approach here. We not only calculate the usual factorizable contributions, but also evaluate the non-factorizable and annihilation type contributions. Besides the current-current operators, the contributions from the QCD and electroweak penguin operators are also taken into account. The pQCD results for the CP-averaged branching ratios are Br(B+→π+η)≈4.1×10−6, Br(B+→π+η′)≈2.4×10−6, and Br(B0→π0η(′))≈0.2×10−6, which agree very well with the measured values or currently available experimental upper limits. We also predict large CP-violating asymmetries in these decays: ACPdir(π±η(′))∼ACPdir(π0η(′))∼−0.35, and ACPmix(π0η(′))∼0.67, but with large errors. The pQCD prediction for ACPdir(π±η) (ACPdir(π±η′)) has the same (opposite) sign with the primary measured values. Further improvements in both theory and experiments are needed to clarify this discrepancy.