Experimental status of theππisoscalarSwave at low energy:f0(600)

The experimental results obtained in the last few years on kaon decays(K$\to2\pi$ and, above all, Ke4 decays) allow a reliable, model independentdetermination of low energy $\pi\pi$ scattering in the S0 wave. Using them and,eventually, other sets of data, it is possible to give a preciseparametrization of the S0 wave as well as to find the scattering length andeffective range parameter. One can also perform an extrapolation to the pole ofthe "$\sigma$ resonance" [$f_0(600)$]. We obtain the results$$a_0^{(0)}=0.233\pm0.013 M^{-1}_\pi,\quad b_0^{(0)}=0.285\pm0.012 M^{-3}_\pi$$and, for the $\sigma$ pole, $$M_\sigma=484\pm17 \mev,\quad\gammav_\sigma/2=255\pm10 {\rm MeV}.$$Comment: Plain TeX;4 figures; improved data used; version to appear in Phys. Rev.