Observation of Bs->K+K- and Measurements of Branching Fractions of   Charmless Two-body Decays of B0 and Bs Mesons in p-pbar Collisions at   sqrt(s)=1.96 TeV
  We search for decays of the type B0(Bs)->h+h'- (where h,h'= K or pi) in 180 pb-1 of p-pbar collisions collected at the Tevatron by the upgraded Collider Detector at Fermilab. We report the first observation of the new mode Bs->K+K- with a yield of 236 +- 32 events, corresponding to (f_s/f_d)*BR(Bs->K+K-)/BR(B0->K+pi-) = 0.46+-0.08(stat.)+-0.07(syst.), where f_s/f_d is the ratio of production fractions of Bs and B0. We find results in agreement with world averages for the B0 modes, and set the following new limits at 90% CL: BR(Bs->K-pi+) < 5.6*10^{-6} and BR(Bs->pi+pi-) < 1.7*10^{-6}. 
CDF Collaboration: A. Abulencia, et al