Branching fractions of B-->h+h'- modes at CDF

I report the analysis of B-->h+h'- decays (where h and h' denote K or pi), in 180 pb-1 of proton-antiproton collisions at s**0.5= 1.96 TeV, with the CDF II detector at the Tevatron Collider. A B-->h+h'- signal was reconstructed at a hadron collider for the first time, in the sample collected by the dedicated trigger on long-lived decays. With about 900 signal events, we observed the new mode Bs-->K+K-, and we measured its branching fraction relative to the B0-->K+pi- mode: (f_s/f_d)*BR(Bs-->K+K-)/BR(B0-->K+pi-)=0.46 +/- 0.08 (stat.) +/- 0.07 (syst.); we also measured the CP-violating decay-rate asymmetry for the B0-->K+pi- mode: ACP=-0.013 +/- 0.078 (stat.) +/- 0.012 (syst.). Since we did not find evidence for rarer modes, we set the following 90% C.L. upper limits on the decay rates: (f_s/f_d)*BR(Bs-->K-pi+)/BR(B0-->K+pi-)<0.08 and BR(Bs-->pi+pi-)/BR(Bs-->K+K-)< 0.05 that are greatly improved with respect to current world averages.

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