S-wave K pi scattering in chiral perturbation theory with resonances

We present a detailed analysis of S-wave K pi scattering up to 2 GeV, makin g use of the resonance chiral Lagrangian predictions together with a suitab le unitarisation method. Our approach incorporates known theoretical constr aints at low and high energies. The present experimental status, with partl y conflicting data from different experiments, is discussed. Our analysis a llows to resolve some experimental ambiguities, but better data are needed in order to determine the cross-section in the higher-energy range, Our bes t fits are used to determine the masses and widths of the relevant scalar r esonances in this energy region. (C) 2000 Elsevier Science B.V. All rights reserved.