Measurement of the relative branching ratio BR(\Xi_c^+ \to p^+ K^-\pi^+)\BR(\Xi_c^+ \to \Xi^- \pi^+ \pi^+)

We report the observation of the Cabibbo suppressed decay Ξc+→pK−π+ using data collected with the FOCUS spectrometer during the 1996–1997 Fermilab fixed target run. We find a Ξc+ signal peak of 202±35 events. We have measured the relative branching ratios BR(Ξ+c→pK−π+)/BR(Ξ+c→Ξ−π+π+)=0.234±0.047±0.022 and BR(Ξ+c→pK̄∗(892)0)/BR(Ξ+c→pK−π+)=0.54±0.09±0.05.