High energy neutrino production by cosmic ray interactions in the Sun

Abstract

The flux of neutrinos originating from cosmic ray interactions with matter in the Sun has been calculated based on Monte Carlo models for high energy particle interactions. The resulting flux at the Earth (within the Sun's solid angle) is higher than the corresponding one from cosmic ray interactions with the Earth atmosphere. The smallness of the absolute rate, however, precludes it as a practical 'standard candle' for neutrino telescopes and limits neutrino oscillation searches. On the other hand, it facilitates dark matter searches based on neutrinos from neutralino annihilation in the Sun.

Rigidity dependent knee and cosmic ray induced high energy neutrino fluxes

“…Previous works that have taken the knee into account have assumed for simplicity that the dominant CR component consists of protons alone, having a spectral change ∆α = 0.3 at E knee . In order to observe the effect of the CR composition on the neutrino fluxes, figure 3 compares the total horizontal atmospheric fluxes (with the prompt charm component calculated with the GBW model) as obtained for different assumptions on the CR spectrum, namely the ∆α = 2/3 rigidity dependent scenario (that corresponds to the results given already in figure 2), the same total CR spectrum but assuming it consists only of protons, and the CR spectrum used in [4,7] (which is assumed to be constituted by protons and has a single spectral index change of ∆α = 0.3 at E knee = 5 × 10 15 eV). The latter CR spectrum has a normalization which is Figure 2: Atmospheric (ν µ +ν µ ) fluxes for the ∆α = 2/3 rigidity dependent scenario (that corresponds to the CR spectrum plotted in figure 1).…”

“…The strong suppression of the ν flux produced by the heavier components implies that the light (H and He) components are still responsible for a large fraction of the neutrinos above their knee, and hence the change in slope of the individual components is also reflected in the change in slope of the neutrino fluxes. Figure 3: Comparison of the total horizontal atmospheric (ν µ +ν µ ) flux for prompt charm/GBW produced by CRs under different assumptions concerning spectrum and composition: the ∆α = 2/3 rigidity dependent scenario that considers the contribution of CR components with charge 1 ≤ Z ≤ 28; the same total CR spectrum but assuming it consists only of protons; and the CR spectrum used in [4,7] (TIG), which also takes only protons into account but has a lower normalization.…”

“…Along directions near the plane of the Milky Way, these diffuse fluxes of galactic neutrinos may overcome the atmospheric neutrino background at energies larger than ∼ 10 14 eV (the actual energy depends on the model adopted for charm production and on the assumed ISM column density, see below), but in the direction orthogonal to the plane they remain below the expected flux from prompt atmospheric neutrinos from charmed particle decays up to the highest energies [7]. Here again the usual simplifying working hypothesis is that the CR flux consists mainly of protons, and only crude attempts have been done trying to generalise the predictions to heavier compositions [9].…”

“…The associated steepening in the induced neutrino fluxes has been obtained in the literature [4,7], but these works usually assume for simplicity that the dominant CR component consists of protons, and only some crude attempts have been done trying to generalise these predictions to heavier compositions [6].…”

“…Another contribution to the diffuse neutrino fluxes produced by CRs are those resulting from the interactions of the CRs present all over the Galaxy with the ambient gas in the inter stellar medium (ISM) [8,9,10,7]. The very low densities in the ISM (n ISM ≃ 1/cm 3 ) imply that essentially all mesons produced decay in this case without suffering any attenuation, and hence the neutrino fluxes are just the conventional ones from π, K and µ decays, and moreover their spectral slopes follow the behaviour of the primary CR spectrum.…”