Abstract
The elastic and radiative π + p scattering are studied in the framework of an effective Lagrangian model for the Δ ++ resonance and its interactions. The finite width effects of this spin-3/2 resonance are introduced in the scattering amplitudes through a complex mass scheme to respect electromagnetic gauge invariance. The resonant pole (Δ ++) and background contributions (ρ 0, σ, Δ, and neutron states) are separated according to the principles of the analytic S-matrix theory. The mass and width parameters of the Δ ++ obtained from a fit to experimental data on the total cross section are in agreement with the results of a model-independent analysis based on the analytic S-matrix approach. The magnetic dipole moment determined from the radiative π + p scattering is \(\mu _{\Delta ^{ + + } } = (6.14 \pm 0.51)\) nuclear magnetons.
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Castro, G.L., Mariano, A. Unstable Particles, Gauge Invariance and the Δ++ Resonance Parameters. Foundations of Physics 33, 719–734 (2003). https://doi.org/10.1023/A:1025692722386
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DOI: https://doi.org/10.1023/A:1025692722386