High energy cosmic-ray interactions with particles from the Sun

Abstract

Cosmic-ray protons with energies above $10^{16}$ eV passing near the Sun may interact with photons emitted by the Sun and be excited to a ${\Delta }^{+}$ resonance. When the ${\Delta }^{+}$ decays, it produces pions which further decay to muons and photons which may be detected with terrestrial detectors. A flux of muons, photon pairs (from ${\pi }^0$ decay), or individual high-energy photons coming from near the Sun would be a rather striking signature, and the flux of these particles is a fairly direct measure of the flux of cosmic-ray nucleons, independent of the cosmic-ray composition. In a solid angle within $15^{\circ }$ around the Sun the flux of photon pairs is about $\text{SI}1.3e-3$ particles/(km${}^2\cdot$yr), while the flux of muons is about $\text{SI}0.33e-3$ particles/(km${}^2\cdot$yr). This is beyond the reach of current detectors like the Telescope Array, Auger, KASCADE-Grande or IceCube. However, the muon flux might be detectable by next-generation air shower arrays or neutrino detectors such as ARIANNA or ARA. We discuss the experimental prospects in some detail. Other cosmic-ray interactions occuring close to the Sun are also briefly discussed.

Comments: 8 pages, 11 figures