Angular distribution of gamma rays produced in proton-proton collisions
Spencer Griffith (Center for Cosmology and AstroParticle Physics (CCAPP), Ohio State University, Columbus, Ohio 43210, USA, Department of Physics, Ohio State University, Columbus, Ohio 43210, USA); John F. Beacom (Center for Cosmology and AstroParticle Physics (CCAPP), Ohio State University, Columbus, Ohio 43210, USA, Department of Physics, Ohio State University, Columbus, Ohio 43210, USA, Department of Astronomy, Ohio State University, Columbus, Ohio 43210, USA); Jung-Tsung Li (Center for Cosmology and AstroParticle Physics (CCAPP), Ohio State University, Columbus, Ohio 43210, USA, Department of Physics, Ohio State University, Columbus, Ohio 43210, USA, Department of Astronomy, Ohio State University, Columbus, Ohio 43210, USA); Annika H.G. Peter (Center for Cosmology and AstroParticle Physics (CCAPP), Ohio State University, Columbus, Ohio 43210, USA, Department of Physics, Ohio State University, Columbus, Ohio 43210, USA, Department of Astronomy, Ohio State University, Columbus, Ohio 43210, USA)
Accurate modeling of how high-energy proton-proton collisions produce gamma rays through the decays of pions and other secondaries is needed to correctly interpret astrophysical observations with the Fermi-LAT telescope. In the existing literature on cosmic-ray collisions with gas, the focus is on the gamma-ray yield spectrum, . However, in some situations, the joint energy and angular distribution can be observed, so one needs instead . We provide calculations of this distribution over the energy range from the pion production threshold to 100 GeV, basing our results on fluka simulations. We provide the results in tabular form and provide a python tool on github to aid in utilization. We also provide an approximate analytic formula that illuminates the underlying physics. We discuss simplified examples where this angular dependence can be observed to illustrate the necessity of taking the joint distribution into account.