Dynamical coupled-channels study of πN→ππN reactions

As a step toward performing a complete coupled-channels analysis of the world data of πN,γ^*N→πN,ηN,ππN reactions, the πN→ππN reactions are investigated starting with the dynamical coupled-channels model developed in Phys. Rev. C 76, 065201 (2007). The channels included are πN,ηN, and ππN which has πΔ,ρN, and σN resonant components. The nonresonant 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 that are dressed by the nonresonant interactions as constrained by the unitarity condition. The data of total cross sections and πN and ππ invariant mass distributions of π⁺p→π⁺π⁺n,π⁺π⁰p and π^-p→π⁺π^-n,π^-π⁰p,π⁰π⁰n reactions from threshold to the invariant mass W=2 GeV can be described to a very large extent. We show the importance of the coupled-channels effects and the strong interference among the contributions from the πΔ,σN, and ρN channels. The large interference between the resonant and nonresonant amplitudes is also demonstrated. Possible future developments are discussed.