Left-hand singularities, hadron form factors and the properties of the sigma meson

By applying analyticity and single-channel unitarity we derive a new formula which is useful to analyze the role of the left-hand singularities in hadron form factors and in the determination of the resonance parameters. Chiral perturbation theory is used to estimate the left-hand cut effects in pi pi scattering processes. We find that in the I, J = 1, 1 channel the left-hand cut effect is negligible and in the I, J = 2, 0 channel the phase shift is dominated by the left-hand cut effect. In the 1, J = 0, 0 channel the left-hand cut contribution to the phase shift has the wrong sign comparing with the experimental data and therefore it necessitates the cr resonance. The new experimental results from the E865 collaboration is crucial in reducing the uncertainty in the determination of the mass and width of the a resonance within our scheme. (C) 2001 Elsevier Science B.V. All rights reserved.Physics, NuclearSCI(E)47ARTICLE273-29469