Observation of the rare decay B^{0}→K_{S}^{0}K^{±}π^{∓}

We report an analysis of charmless hadronic decays of neutral B mesons to the final state KS0K±π∓, using a data sample of (465±5)×106 BB̅ events collected with the BABAR detector at the Υ(4S) resonance. We observe an excess of signal events with a significance of 5.2 standard deviations including systematic uncertainties and measure the branching fraction to be B(B0→KS0K±π∓)=(3.2±0.5±0.3)×10-6, where the uncertainties are statistical and systematic, respectively.