Examination of Flavor Symmetry in $B, B_s \to K \pi$ Decays
  We study a relation between the weak phase $\gamma$ and the rates and CP asymmetries of several $K \pi$ decays of $B^+$, $B^0$, and $B_s$, emphasizing the impact of the latter measurements. Current data indicate large SU(3) breaking in the strong phases or failure of factorization (including its application to penguin amplitudes) in $K \pi$ modes of $B^0$ and $B_s$. SU(3) and factorization only remain approximately valid if the branching ratio for $B_s \to K^- \pi^+$ exceeds its current value of $(5.27 \pm 1.17) \times 10^{-6}$ by at least 42%, or if a parameter $\xi$ describing ratios of form factors and decay constants is shifted from its nominal value by more than twice its estimated error. 
Cheng-Wei Chiang, Michael Gronau, and Jonathan L. Rosner