The Mixing Angle of the Lightest Scalar Nonet

Nucl.Phys.A727:353-369,2003 We show that the \kappa, a_0(980), \sigma and the f_0(980) resonances constitute the lightest scalar nonet in three different and complementary ways. First, by establishing the continuous movement of the poles from the physical to a SU(3) limit. Second, by performing an analysis of the couplings of the scalar mesons to pairs of pseudoscalars and third, by analysing the couplings of the scalars with meson-meson SU(3) scattering eigenstates. Every of the last two methods agree that the mixing angle between the singlet and the octet I=0 states is \theta= 19^o\pm 5 degrees, so that the \sigma is mainly the singlet and the f_0(980) the isosinglet octet state.