Meson photo-production in GEANT4 for Eγ=0.225–3.0 GeV using the γ+p→n+π+ reaction

In a previous study, we compared experimental data of the total and angular differential cross sections of π 0 photo-production off the proton to theoretical models implemented in version 9.6.p02 of the GEANT4 Monte Carlo simulation toolkit (Amar et al. in Eur Phys J A 55:62, 2019). This paper describes a similar work but for the exclusive and differential cross sections of the π + photo-production off the proton. The Chiral Invariant Phase Space (CHIPS) and Bertini Cascade (BERT) models were compared to the experimental data from the CEBAF Large Acceptance Spectrometer (CLAS) of Jefferson Lab and the phenomenological Scattering Analysis Interactive Dial-in (SAID) model. Relativistic Breit–Wigner fits were used to compare the description of the nucleon resonance region up to 3 GeV from SAID, CLAS and CHIPS. As observed in the π 0 case, the CHIPS model provides a reasonable description of the invariant mass distribution while the limited tabulated data set of the BERT model is not adequate. Furthermore, the γ p → n π + differential cross sections d σ / d Ω show significant differences between CHIPS and both CLAS and SAID data pointing to some needed improvements in its physics.