Observation of Two Narrow States Decaying intoΞc+γandΞc0γ

We report the first observation of two narrow charmed strange baryons decaying to {Xi}{sup +}{sub c}{gamma} and {Xi}{sup 0}{sub c}{gamma} , respectively, using data from the CLEO II detector at the Cornell Electron Storage Ring. We interpret the observed signals as the {Xi}{sup +{prime}}{sub c}thinsp( c{l_brace}su{r_brace}) and {Xi}{sup 0{prime}}{sub c}thinsp( c{l_brace}sd{r_brace}) , the symmetric partners of the well-established antisymmetric {Xi}{sup +}{sub c}thinsp(c[ su]) and {Xi}{sup 0}{sub c}thinsp(c[ sd]) . The mass differences M({Xi}{sup +{prime}}{sub c}){minus}M( {Xi}{sup +}{sub c}) and M({Xi}{sup 0{prime}}{sub c}){minus}M( {Xi}{sup 0}{sub c}) have been measured to be 107.8{plus_minus}1.7{plus_minus}2.5 and 107.0{plus_minus}1.4{plus_minus}2.5 MeV /c{sup 2} , respectively. {copyright} {ital 1999} {ital The American Physical Society }