Abstrakt
We report results from a study of the spin and parity of Xi(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 Xi(c)(2970)(+) -> Xi(c) (2645)(0)pi(+) -> Xi c(+) pi(-)pi(+) are analyzed to determine the spin of this charmed-strange baryon.
The angular distributions strongly favor the Xi(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 Xi(c) (2970)(+) decay branching fractions R= B[Xi(c) (2970)(+) -> Xi(c)(2645)(0)(pi)+]/B[Xi(c)(2970)(+) -> Xi('0)(c)pi(+)] 1..67 +/- 0.29(stat)(-0.09)(+0.15)(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.