Abstract

Peculiarities of obtaining parameters for broad multichannel resonances from data are discussed analyzing the experimental data on processes pi pi ->pi pi, K (K) over bar in the scalar channel in a model-independent approach based on analyticity and unitarity and using an uniformization procedure. It is shown that one can obtain a good description of the pi pi scattering data from the threshold up to 1.89 GeV with values of resonance parameters cited in the PDG tables as preferred. However, in this case the representation of the pi pi background is not satisfactory and the data on the coupled process pi pi ! K (K) over bar are not well described, above 1.15 GeV even qualitatively. The combined analysis of the considered coupled processes is needed, which is also carried out satisfactorily. Then both above-indicated deficiencies related to the one-channel analysis are removed. The most important change concerns parameters of the f(0)(600) which are now in some accordance with the prediction by Weinberg on the basis of mended symmetry. The obtained pi pi scattering length agrees well with the values extracted from the data on K-e4 decay and DIRAC experiment and also with results from ChPT.