Re-analysis of ππ/Kπ phase shift and existence of σ(600)/κ(900)-particle

Re-analyzing the old phase shift data of I=0, ππ(I=1/2,Kπ) scattering, we show an evidence for existence of the σ-particle(κ-particle) with a comparatively light mass, which has been missing for a long time: In the analysis we have applied a new method of interfering Breit-Wigner amplitudes, which makes the scattering amplitude parametrized in terms of only physical quantities, mass and width of resonant particles, in conformity with unitarity. We have introduced phenomenologically a background phase shift δBG of repulsive core type. The χ2-fits of the both ππ- and Kπ-phase shifts are improved greatly with the δBG over the conventional fits without it