Branching ratio and CP asymmetry of $B_s \to \pi^+ \pi^-$ decays in the   perturbative QCD approach
  In this paper, we calculate the decay rate and CP asymmetry of the $B_s \to \pi^+\pi^-$ decay in perturbative QCD approach with Sudakov resummation. Since none of the quarks in final states is the same as those of the initial $B_s$ meson, this decay can occur only via annihilation diagrams in the standard model. Besides the current-current operators, the contributions from the QCD and electroweak penguin operators are also taken into account. We find that (a) the branching ratio is about $4 \times 10^{-7}$; (b) the penguin diagrams dominate the total contribution; and (c) the direct CP asymmetry is small in size: no more than $3% $; but the mixing-induced CP asymmetry can be as large as ten percent testable in the near future LHC-b experiments. 
Ying Li, Cai-Dian Lu, Zhen-Jun Xiao, Xian-Qiao Yu