Theoretical study of the Ξ(1620) and Ξ(1690) resonances in Ξ_c → π~+MB decays

摘要

Nonleptonic weak decays of Ξ_c into π~+ and a meson (M)-baryon (B) final state, MB, are analyzed from the viewpoint of probing S = -2 baryon resonances, i.e., Ξ(1620) and Ξ(1690), of which spin-parity and other properties are not well known. We argue that the weak decay of Ξ_c is dominated by a single quark-line diagram, preferred by the Cabibbo-Kobayashi-Maskawa coefficient, color recombination factor, the diquark correlation, and the kinematical condition. The decay process has an advantage of being free from meson resonances in the π~+M invariantmass distribution. The invariant mass distribution of the meson-baryon final state is calculatedwith three different chiral unitary approaches, assuming that the Ξ(1620) and Ξ(1690) resonances have J~P = 1/2~-. It is found that a clear peak for the Ξ(1690) is seen in the πΞ and KΛ spectra. We also suggest that the ratios of the πΞ, KΛ, and KΣ final states are useful to distinguish whether the peak is originated from the Ξ(1690) resonance or it is a KΣ threshold effect.