Effect of decay cascade via an intermediate resonance in the <i>γp</i> → <i>π</i> ⁰ <i>ηp</i> reaction*

Abstract The reaction has been investigated by the CBELSA/TAPS collaboration, revealing a narrow structure in the invariant mass distributions at a mass of 1700 MeV. In this study, we explore the possibility of the narrow structure being caused by a decay cascade via an intermediate nucleon resonance decaying to final states. The candidates for the intermediate nucleon resonances are and , with masses near the observed structure. We considered the t -channel ρ - and ω -exchange diagrams, u -channel nucleon-pole exchange diagram, contact term, and s -channel pole diagrams of the nucleon, Δ, along with the nucleon resonances when constructing the reaction amplitudes, to reproduce the stripped individual contribution of the narrow structure. Our analysis indicates that the signature strength of the decay cascade is too weak to reach the experimental curve of the narrow structure due to the small decay branching ratio of to . Although the decay cascade can qualitatively reproduce the experimental curve of the invariant mass distributions, its cross-section width is much larger than that of the corresponding experimental curve. Therefore, we conclude that the decay cascade via an intermediate nucleon resonance cannot be the reason for the narrow structure in the invariant mass distributions of the reaction.