Lowest resonance in QCD from low-energy data

Abstract

We worked out a generalization of su(2) chiral perturbation theory, including a perturbative singlet scalar field. The approach suggests that the prediction for sensible low-energy observables converge faster towards their physical value. The physical mass and width of the scalar particle are obtained through a simultaneous analysis of the pion vector form factor and the ¿¿¿p 0 p 0 cross section. Both values are statistically consistent with the ones obtained by using Roy equations in p-p scattering. In addition we find indications that the photon-photon-singlet coupling is quite small