Meson Photo-Production in {\Geant} for $E_\gamma =0.225-3.0$~GeV Using the $\gamma + p \rightarrow p + \pi ^0$ reaction

The purpose of this study is to compare experimental data and theoretical models implemented in version 9.6.p02 of the {\Geant} Monte Carlo simulation toolkit for the exclusive and differential cross sections of $\pi^0$ photo-production. The data from 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 of the $\Delta(1232)$, N*(1520), N*(1650) and N*(1875) resonances give agreements to within 3\% for the mass of each resonance. BERT does not allow for an accurate description of the energy distribution. The angular distributions of the cross sections show significant differences between CHIPS and both CLAS and SAID. The physics in CHIPS appears to be correct but it needs further development for the individual resonances contributions that could be useful since it is also the only model able to treat electromagnetically induced meson production for $A>1$.