The Dominance of Nucleon Resonances in Neutrino and γ-Ray Production from Photonuclear Interactions in Astrophysics

The aim of this paper is to present a more complete analysis of the theoretical concepts and experimental aspects of the physics of photoproduction interactions involving nuclei. We thus determine the relative contributions of excited nucleon, pπ, pππ resonances and ρ,η, ω and K production and the subsequent decay channels leading to neutrino and γ-ray production. This treatment is based in large part on the most recent and extensive empirical data on particle photoproduction interactions off protons and He nuclei. It is shown that in astrophysical sources with steep proton energy spectra the Δ(1232) resonance channel clearly dominates. However, a blend of N* resonances at ∼1400 GeV can contribute as much as 20% to the neutrino flux. It is further found that γ-He interactions, assuming the cosmological abundance of He, produce approximately 10% of the pions as compared with γρ interactions.