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Resumen:
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The experimental results obtained in the last few years on kaon decays (K ? 2 ? and, above all, Ke4 decays) allow a reliable, model-independent determination of low energy ? ? scattering in the S0 wave. Using them and, eventually, other sets of data, it is possible to give a precise parametrization of the S0 wave as well as to find the scattering length and effective range parameter. One can also perform an extrapolation to the pole of the ‘‘sigma resonance’’ [f_0(600)]. We obtain the results a_(0)^(0) = 0,233 ± 0,013M_(?)^(-1), b_(0)^(0)=0,285 ± 0,012M_(?)^(-3), and, for the ? pole, M_(?) = 484 ± 17 MeV, ?_? =255 ± 10 MeV.
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