Abstract
The composition in terms of nuclear species of the primary cosmic ray flux is largely uncertain in the knee region and above, where only indirect measurements are available. The predicted fluxes of high-energy leptons from cosmic ray air showers are influenced by this uncertainty. Different models have been proposed. Similarly, these uncertainties affect the measurement of lepton fluxes in very large-volume neutrino telescopes. Uncertainties in the cosmic ray interaction processes, mainly deriving from the limited amount of experimental data covering the particle physics at play, could also produce similar differences in the observable lepton fluxes and are affected as well by large uncertainties. In this paper we analyse how considering different models for the primary cosmic ray composition affects the expected rates in the current generation of very large-volume neutrino telescopes (ANTARES and IceCube). This is tested comparing two possible models of cosmic ray composition, but the same procedure can be expanded to different possible combinations of cosmic ray abundances. We observe that a certain degree of discrimination between composition fits can be already achieved with the current IceCube data sample, even though in a model-dependent way. The expected improvements in the energy reconstruction achievable with the next-generation neutrino telescopes is be expected to make these instruments more sensitive to the differences between models.
Highlights
The composition in terms of nuclear species of the primary cosmic ray flux is largely uncertain in the knee region and above, where only indirect measurements are available
Extensive air-shower arrays indirectly measure the cosmic ray flux at Earth by observing the shower products arriving on the ground, coming from the electromagnetic component and the hadronic component—the latter being addressed by measuring muons penetrating underground
The direct measurements obtained by satellite and balloon flights, using magnetic deflection, allow accessing the mass spectrum of primary cosmic ray (CR) up to some tens of TeV; the per-species power-law behaviour could be extrapolated to higher energy, but the spectral features present above hundreds TeV/few PeV energies appear
Summary
Since the decay kinematics are well known, the overall flux is determined mostly by the primary flux and by the production efficiency and interaction probability of the parent hadrons Our knowledge of the former is affected by large uncertainties, both for what concerns the spectral behaviour of the individual components of the flux and the nature itself of the primary particles species. The latter, i.e. the description of the primary hadronic interaction and the description of the further interactions of these hadrons as the cascade of particles showers down in the atmosphere, is rather uncertain in the energy range above a few hundred GeV.
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