Parametrization of the nucleus-nucleus γ -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 γ-rays and e ± pairs from nuclear collisions with energy per nucleon below the π-meson production threshold. I use publicly available experimental data to parametrize these two channels' γ-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 Tp ≤ 100 A GeV and agree reasonably well with the available experimental data. The new parametrizations allow, for the first time, accurate studies of astrophysical γ-rays below 1 GeV.

Exploring the shape of the γ-ray spectrum around the “π0-bump”

“…Despite the lack of a self-consistent theory of the subthreshold pion production, the cross-sections of many heavy ion reactions are well studied experimentally (Cassing et al 1990;Metag 1993). Recently, these cross-sections have been parametrised by simple analytical expressions (Kafexhiu 2016). In Fig.7 the available experimental data are shown together with parametrisations of the neutral pion production cross-sections for p -4 He, p -12 C, and 12 C -12 C interactions.…”

“…However in the case of "heavy" compositions of both CRs and the ambient gas dominated by nuclei, these processes could play a non-negligible role in the formation of the overall γ-ray spectrum below 100 MeV. The Cross sections for hard photon production are parametrised by Kafexhiu (2016).…”

“…π 0 production cross sections for the p + p, p + 4 He, p + 12 C and 12 C + 12 C interactions. The experimental points are shown together with the paramerizations of cross-sections fromKafexhiu (2016).…”

Gamma-ray emission of hot astrophysical plasma

“…Nevertheless, for a purpose of consistency, we present here the production rates of π 0 -mesons from nuclei heavier than hydrogen. For these calculations we use the recent parametrizations [39] of nucleus-nucleus cross sections including the so-called subthreshold pion production. In Fig.…”

Probing maximum energy of cosmic rays in SNR through gamma rays and neutrinos from the molecular clouds around SNR W28

“…where F π (x, E N ) is same as equation (9), w AB is the number of wounded nucleons and σ AB inel is inelastic cross section in nucleus-nucleus interaction. In addition the threshold energy per nucleon has to be replaced by E th [47]. For nucleus-nucleus interaction, the reaction cross section reads [46,63]…”