Parametrization of the nucleus-nucleus <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>γ</mml:mi></mml:math>-ray production cross sections below 100 GeV/nucleon: Subthreshold pions and hard photons

Abstract

``Subthreshold pions'' and so-called ``hard photons'' are two important channels for producing less than 1 GeV $\ensuremath{\gamma}$ rays and ${e}^{\ifmmode\pm\else\textpm\fi{}}$ pairs from nuclear collisions with energy per nucleon below the $\ensuremath{\pi}$-meson production threshold. I use publicly available experimental data to parametrize these two channels' $\ensuremath{\gamma}$-ray and ${e}^{\ifmmode\pm\else\textpm\fi{}}$ 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 ${T}_{p}\ensuremath{\le}100A$ GeV and agree reasonably well with the available experimental data. The new parametrizations allow, for the first time, accurate studies of astrophysical $\ensuremath{\gamma}$ rays below 1 GeV.