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, and pππ resonances and ρ, η, ω and K production, as well as 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 produce approximately 10% of astrophysical pions, as compared with γp interactions.