### ?

## First Determination of the Spin and Parity of a Charmed-Strange Baryon, Ξc(2970)+

We report results from a study of the spin and parity of Ξ*c*(2970)+ using a 980 fb−1 data sample collected by the Belle detector at the KEKB asymmetric-energy *e*+*e*− collider. The decay angle distributions in the chain Ξ*c*(2970)+→Ξ*c*(2645)0*π*+→Ξ+*c**π*−*π*+ are analyzed to determine the spin of this charmed-strange baryon. The angular distributions strongly favor the Ξ*c*(2970)+ spin *J*=1/2 over 3/2 or 5/2, under an assumption that the lowest partial wave dominates in the decay. We also measure the ratio of Ξ*c*(2970)+ decay branching fractions *R*=B[Ξ*c*(2970)+→Ξ*c*(2645)0*π*+]/B[Ξ*c*(2970)+→Ξ′0*c**π*+]=1.67±0.29(stat.)+0.15−0.09(syst.)±0.25(IS), where the last uncertainty is due to possible isospin-symmetry-breaking effects. This *R* value favors the spin-parity *J**P*=1/2+ with the spin of the light-quark degrees of freedom *s**l*=0. This is the first determination of the spin and parity of a charmed-strange baryon.