First determination of the spin and parity of the charmed-strange baryon ξc (2970)+.

Abstract

We report results from a study of the spin and parity of Ξcð2970Þþ using a 980 fb−1 data sample collected by the Belle detector at the KEKB asymmetric-energy eþe− collider. The decay angle distributions in the chain Ξcð2970Þþ → Ξcð2645Þ0πþ → Ξþ c π−πþ are analyzed to determine the spin of this charmed-strange baryon. The angular distributions strongly favor the Ξcð2970Þþ spin J ¼ 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 Ξcð2970Þþ decay branching fractions R¼B½Ξcð2970Þþ→Ξcð2645Þ0πþ=B½Ξcð2970Þþ→Ξ00 c πþ¼ 1.670.29ðstatÞ þ0.15 −0.09 ðsystÞ0.25ðISÞ, where the last uncertainty is due to possible isospin-symmetrybreaking effects. This R value favors the spin-parity JP ¼ 1=2þ with the spin of the light-quark degrees of freedom sl ¼ 0. This is the first determination of the spin and parity of a charmed-strange baryon.