The Chiral approach of the Ξ(1620) and Ξ(1690) resonances in the Ξ c+ → π⁺ π⁺ Ξ⁻ decay

Abstract

We study s-wave meson-baryon interactions with strangeness S = −2 in a coupledchannels chiral approach incorporating not only the leading Weinberg-Tomozawa term in the Lagrangian, but also the Born terms and next-to-leading order contributions. With our model we fit the experimental data set of the nonleptonic X+c ! p+p+X− weak decay from the Belle Collaboration, where the observation of the double strange baryons X(1620) and X(1690) in their decay to p+X− was reported. We calculate the invariant mass distribution of the p+X− final state, showing that our theoretical prediction is capable of explaining the experimental data by reproducing the two resonance peaks. Regarding the pole content, we are able to dynamically generate two poles not far away from the known experimental values of the X(1620) and X(1690) states. In our approach these resonances have a molecular nature, where the lowest one strongly couples to the pX channels, while the second pole couples more strongly to the ¯KS channels.