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The K-matrix approach to the Delta - resonance mass splitting and isospin violation in low-energy pi-N scattering

A. B. Gridnev·I. Horn·W. J. Briscoe·I. I. Strakovsky
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Abstract

The experimental data on pi N scattering in the elastic energy region T_pi < 250 MeV are analyzed within the multichannel K-matrix approach with effective Lagrangians. Isospin invariance is not assumed in this analysis and the physical values for masses of the involved particles are used. The corrections due to pi^+- pi^0 and p-n mass differences are calculated and found to be in a reasonable agreement with the NORDITA results. Analysis shows the good description of the all experimental observables. From the data, new values for mass and width of the Delta^0 and Delta^{++} resonances were obtained. The isospin symmetric version gives phase shifts values close to the new solution for the pi-N elastic scattering amplitude FA02 by the GW group based on the latest experimental data. Our analysis leads to a considerably smaller < 1% isospin violation in the energy interval T_pi ~ 30-70 MeV as compared to 7% in some older analyses, however, it does confirm recent calculations based on chiral perturbation theory.

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A. B. Gridnev, I. Horn, W. J. Briscoe, I. I. Strakovsky. 2006-05-22. The K-matrix approach to the Delta - resonance mass splitting and isospin violation in low-energy pi-N scattering. https://doi.org/10.1134/s1063778806090122

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