Observation of a Narrow State Decaying intoΞc+π−

Using data recorded by the CLEO-II detector at Cornell Electron Storage Ring (CESR), we report the first observation of a narrow state decaying into ${\Xi }_c^{+}{\pi }^{-}$. The state has mass difference $M\left({\Xi }_c^{+}{\pi }^{-}\right)-M\left({\Xi }_c^{+}\right)$ of 178.2 ± 0.5 ± 1.0 MeV/${\mathit{c}}^2$, and a width of <5.5 MeV/${\mathit{c}}^2$ (90% confidence level limit). The most likely explanation of this new state is that it is the ${\Xi }_c^{*0\mathrm{}}$, the $J^P={\frac{3}{2}}^{+}$ spin excitation of the ${\Xi }_c^0$ charmed baryon.