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Experiments are being contemplated to measure pi - pi cross sections in the processes; pi /sup +/ + p yields 2 pi /sup +/ + n, pi /sup -/ p yields pi /sup +/ + pi /sup -/ n, pi /sup -/ p yields pi /sup -/ + pi /sup 0/ + p, an d pi /sup +/ + p yields pi /sup +/ + pi /sup 0/ + p. The cross sections are estimated by use of the theoretical resonance prediction for sigma /sub pi pi / in the I = I state. The same processes are considered in terrus of the statistical model. By comparing the two results, suitable resions are found in the phase space for the experiments to be performed. (W.D.M.).
It is shown that the 4pi intermediate state in pi-pi scattering plays an important role in determining the position and perhaps even the existence of the pi-pi resonance. This large effect occurs by virtue of the pi resonance. Quantitative estimates are given. The effect of this result on the nucleon form factors is briefly discussed and a simple model for these functions is proposed. The possibility of higher energy pion resonances is also considered. (Author).
As a step toward performing a complete coupled-channels analysis of the world data of pi N, gamma^* N --> pi N, eta N, pi pi N reactions, the pi N --> pi pi N reactions are investigated starting with the dynamical coupled-channels model developed in Phys. Rev. C76, 065201 (2007). The channels included are pi N, eta N, and pi pi N which has pi Delta, rho N, and sigma N resonant components. The non-resonant amplitudes are generated from solving a set of coupled-channels equations with the meson-baryon potentials defined by effective Lagrangians. The resonant amplitudes are generated from 16 bare excited nucleon (N^*) states which are dressed by the non-resonant interactions as constrained by the unitarity condition. The available total cross section data of pi^+ p --> pi^+ pi^+ n, pi^+ pi^0 and pi^- p --> pi^+ pi^- n, pi^- pi^0 n, pi^0 pi^0 n can be reproduced to a very large extent both in magnitudes and energy-dependence. Possible improvements of the model are investigated, in p.