Phenomenological Description of Double-Pion Photoproduction

Abstract

Double pion photoproduction off proton targets is studied, in the framework of an Effective Lagrangian approach at tree level, based on the coupling of photons and pions to nucleons and resonances. We consider N, Δ(1232), N(1440), N(1520) and N(1535) as intermediate baryonic states and ρ-meson as the intermediate 2π resonance. The general form of the amplitude is presented and total cross sections of the γp → π+π− p, γp → π0π0p and γp → π +π0n processes are evaluated up to Eγ = 800 MeV. We fit our theoretical calculation to the experimental data and extract some previously unknown parameters. Furthermore, single pion photoproduction is studied and analysis of the axial anomaly using the γπ+ → π+π 0 reaction near threshold is presented.