$CP$ violation for $B^{0}\rightarrow \rho^{0}(\omega)\rho^{0}(\omega)   \rightarrow \pi^+\pi^-\pi^+\pi^-$ in QCD factorization
  In the QCD factorization (QCDF) approach we study the direct $CP$ violation in $\bar{B}^{0}\rightarrow\rho^0(\omega)\rho^0(\omega)\rightarrow\pi^+\pi^-\pi^+\pi^-$ via the $\rho-\omega$ mixing mechanism. We find that the $CP$ violation can be enhanced by double $\rho-\omega$ mixing when the masses of the $\pi^+\pi^-$ pairs are in the vicinity of the $\omega$ resonance, and the maximum $CP$ violation can reach 28{\%}. We also compare the results from the naive factorization and the QCD factorization. 
Gang L\"u, Jia-Qi Lei, Xin-Heng Guo, Zhen-Hua Zhang, Ke-Wei Wei
hep-ph