Observation of the Cabibbo-suppressed charmed baryon decay ${\Lambda }_c^{+}\to p\phi$

We report the observation of the Cabibbo-suppressed decays ${\Lambda }_c^{+}\to p{K}^{-}{K}^{+}$ and ${\Lambda }_c^{+}\to p\phi$ using data collected with the CLEO II detector at CESR. The latter mode, observed for the first time with significant statistics, is of interest as a test of color suppression in charm decays. We have determined the branching ratios for these modes relative to ${\Lambda }_c^{+}\to p{K}^{-}{\pi }^{+}$ and compared our results with theory.