Observation of B0 (s) ---> K+ K- and Measurements of Branching Fractions of Charmless Two-body Decays of B0 and B0(s) Mesons in anti-p p Collisions at s**(1/2) = 1.96-TeV

The authors search for decays of the type B{sub (s)}{sup 0} {yields} h{sup +}h'{sup -} (where h,h' = K or {pi}) in 180 pb{sup -1} of data collected by the CDF II detector at the Fermilab Tevatron. They observe the new mode B{sub s}{sup 0} {yields} K{sup +}K{sup -} with a yield of 236 {+-} 32 events, corresponding to (f{sub s}/f{sub d}) x {Beta}(B{sub s}{sup 0} {yields} K{sup +}K{sup -})/{Beta}(B{sup 0} {yields} K{sup +}{pi}{sup -}) = 0.46 {+-} 0.08(stat.) {+-} 0.07(syst.), where f{sub s}/f{sub d} is the ratio of production fractions of B{sub s}{sup 0} and B{sup 0}. They find results in agreement with world averages for the modes B{sup 0} {yields} {pi}{sup +}{pi}{sup -} and B{sup 0} {yields} K{sup +}{pi}{sup -}, and set the following upper limits at 90% CL: {Beta}(B{sup 0} {yields} K{sup +}K{sup -}) < 1.8 x 10{sup -6}, {Beta}(B{sub s}{sup 0} {yields} K{sup -}{pi}{sup +}) < 5.6 x 10{sup -6}, and {Beta}(B{sub s}{sup 0} {yields} {pi}{sup +}{pi}{sup -}) < 1.7 x 10{sup -6}