Observation of new charmless decays of bottom hadrons

We search for new charmless decays of neutral b-hadrons to pairs of charged hadrons with the upgraded Collider Detector at the Fermi lab Tevatron. Using a data sample corresponding to 1 fb(-1) of integrated luminosity, we report the first observation of the B(s)(0) -> K(-)pi(+) decay, with a significance of 8.2 sigma, and measure B(B(s)(0) -> K(-)pi(+)) = (5.0 +/- 0.7 (stat.) +/- 0.8 (syst.)) x 10(-6). We also report the first observation of charmless b-baryon decays in the channels A(b)(0) -> p pi(-) and A(0)(b) -> pK(-) with significances of 6.0 sigma and 11.5 sigma respectively, and we measure B(A(b)(0) -> p pi(-)) = (3.5 +/- 0.6 (stat.) +/- 0.9 (syst.)) x 10(-6) and B(A(b)(0) -> pK(-)) = (5.6 +/- 0.8 (stat.) +/- 1.5 (syst.)) x 10(-6). No evidence is found for the decays B(0) -> K(+)K(-) and B(s)(0) -> and we set an improved upper limit B(B(s)(0) -> pi(+)pi(-)) < 1.2 x 10(-6) at the 90% confidence level. All quoted branching fractions are measured using B(B(0) -> K(+)K(-)) as a reference.