Observation of a Narrow State Decaying into $\Xi_c^+\pi^-$

Using data recorded by the CLEO-II detector at CESR, we report the first observation of a narrow state decaying into $\Xi_c^+\pi^-$. The state has mass difference $M(\Xi_c^+\pi^-)-M(\Xi_c^+)$ of $178.2\pm0.5\pm1.0$ $\rm{MeV/c^2}$, and a width of $<5.5$ $\rm{MeV/c^2}$ (90\% confidence level limit). The most likely explanation of this new state is that it is the $J=\32$ spin excitation of the $\Xi_c^0$ charmed baryon.