This work contains a study of the meson-baryon interaction in the S = −1 sector by means of a chiral S U(3) Lagrangian up to next-to-leading order (NLO) and implementing unitarization in coupled channels. In order to get more reliable values of the parameters which are present in the model, we performed several fits which take a large set of experimental scattering data in different two-body channels, threshold branching ratios, and the precise SIDDHARTA values of the energy shift and width of

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... aonic hidrogen into consideration. In previous studies, we had shown that the K − p → KΞ reactions are especially sensitive to the next to Weinberg-Tomozawa (WT) corrections in the hierarchy. In addition, we pointed out the need to employ processes which are described by pure isospin amplitudes as a tool to discern which models are more realistic among those which give small values for the χ 2 in the fits. Following the former suggestion, we present results which include data from K − p → ηΛ, ηΣ reactions which have pure isospin I = 0 and I = 1 component respectively. Finally, to check the goodness of the new obtained parametrization of the model, we present a prediction for another process that filters the I = 1 isospin component: the pure I = 1 K − L p → K + Ξ 0 reaction which could be measured at the proposed secondary K 0 L beam at Jlab. a