Parametrization of gamma-ray production cross-sections for pp   interactions in a broad proton energy range from the kinematic threshold to   PeV energies
  Using publicly available Monte Carlo codes as well as compilation of published data on p--p interactions for proton kinetic energy below 2 GeV, we parametrize the energy spectra and production rates of $\gamma$-rays by simple but quite accurate ($\leq 20 \%$) analytical expressions in a broad range from the kinematic threshold to PeV energies. 
Ervin Kafexhiu, Felix Aharonian, Andrew M. Taylor, Gabriela S. Vila
astro-ph.HE nucl-ex