Isospin symmetry breaking effects for the mode ${B}\rightarrow ππ(K)$ in Perturbative QCD
We calculate the direct $CP$ violation for the decay process of ${B}^{0}\rightarrow π^{0}π^{0}$, ${B}^{+}\rightarrow π^{0}π^{+}$, ${B}^{0}\rightarrow K^{0}π^{0}$ and ${B}^{+}\rightarrow K^{+}π^{0}$ via isospin symmetry breaking effects from the $π^{0}-η-η'$ mixing mechanism in perturbative QCD approach. Isospin symmetry breaking originates from the electroweak interaction and the u-d quark mass difference through the strong interaction which are known to be tiny. However, we find that isospin symmetry breaking at the leading order changes the $CP$ violation from the new strong phases. Our calculation results for the $CP$ violation are within or including the range of experimental results. We also compare our results with those from the QCD factorization and the perturbative QCD schemes without regard to isospin symmetry breaking effects.