Observation of B(s)(0)-> K(+)K(-) and measurements of branching fractions of charmless two-body decays of B(0) and B(s)(0) mesons in p (p)over bar collisions at root s=1.96 TeV

We search for decays of the type B((s))(0)-> h(+)h('-) (where h,h(')=K or pi) in 180 pb(-1) of (p) over barp collisions collected at the Tevatron by the upgraded Collider Detector at Fermilab. We report the first observation of the new mode B(s)(0)-> K(+)K(-) with a yield of 236 +/- 32 events, corresponding to (f(s)/f(d))xB(B(s)(0)-> K(+)K(-)))/B(B(0)-> K(+)pi(-))=0.46 +/- 0.08(stat)+/- 0.07(syst), where f(s)/f(d) is the ratio of production fractions of B(s)(0) and B(0). We find results in agreement with world averages for the B(0) modes, and set the following new limits at 90% C.L.: B(B(s)(0)-> K(-)pi(+))< 5.6x10(-6) and B(B(s)(0)->pi(+)pi(-))< 1.7x10(-6)