The Ξ(1620) and Ξ(1690) molecular states from S = -2 meson-baryon interaction up to next-to-leading order

We have studied the meson-baryon interaction in the neutral S = - 2 sector using an extended Unitarized Chiral Perturbation Theory, which takes into account not only the leading Weinberg-Tomozawa term (as all the previous studies in S = - 2 sector), but also the Born terms and next-to-leading order contribution. Based on the SU(3) symmetry of the chiral Lagrangian we took most of the model parameters from the BCN model [1], where these were fitted to a large amount of experimental data in the neutral S = - 1 sector. We have shown that our approach is able to generate dynamically both Ξ (1620) and Ξ (1690) states in very reasonable agreement with the data, and can naturally explain the puzzle with the decay branching ratios of Ξ (1690). Our results clearly illustrate the reliability of chiral models implementing unitarization in coupled channels and the importance of considering Born and NLO contributions for precise calculations.