First Observation of B-s(0)->(DsK -/+)-K-+/- and Measurement of the Ratio of Branching Fractions B(B-s(0)->(DsK -/+)-K-+/-)/B(B-s(0)-> D-s(+)pi(-))

A combined mass and particle identificationfit is used to make the first observation of the decay B- s(0)->(DsK -/+)-K-+/- and measure the branching fractionof B- s(0)->(DsK -/+)-K-+/- relative to B- s(0)-> D- s(+)pi(-). This analysis uses 1.2 fb(-1) integrated luminosity of pp collisions at s=1.96 TeV collected with the CDF II detector at the Fermilab Tevatroncollider. We observe a B- s(0)->(DsK -/+)-K-+/- signal with a statistical significance of 8.1 sigma and measure B(B- s(0)->(DsK -/+)-K-+/-)/B(B- s(0)-> D- s(+)pi(-))=0.097 +/- 0.018(stat)+/- 0.009(syst).