Parametrization of the nucleus-nucleus gamma-ray production cross sections below 100 GeV/nucleon: Subthreshold pions and hard photons

摘要

"Subthreshold pions" and so-called "hard photons" are two important channels for producing less than 1 GeV gamma rays and e(+/-) pairs from nuclear collisions with energy per nucleon below the pi-meson production threshold. I use publicly available experimental data to parametrize these two channels' gamma-ray and e(+) production cross sections and extend the pion contribution to these particles spectra at higher energies using their corresponding spectra from pp interactions. These parametrizations are valid for collision energy T-p <= 100A GeV and agree reasonably well with the available experimental data. The new parametrizations allow, for the first time, accurate studies of astrophysical gamma rays below 1 GeV.