Investigating cosmic ray elemental spectra and the atmospheric muon neutrino flux

Abstract

Recent direct measurements of cosmic ray elemental spectra have indicated various new spectral features. Spectral hardening, at ∼200 GV, has repeatedly been reported throughout the past decade by various satellite and balloon-borne instruments. Subsequent spectral softening, at ∼10 TeV, has begun to gain support more recently as direct measurements reach higher energies. In this analysis, cosmic ray elemental spectra between ∼103 - 108 GeV are considered to examine the impact of this new data on the calculated all-particle spectrum, 〈ln(A)〉 trends, and atmospheric muon neutrino flux. The cosmic ray spectra are modeled as a superposition of 4 acceleration sources with rigidity dependent acceleration limits. By grouping elements based on their shared rigidity dependencies recently observed by direct measurement experiments, the fitting procedure is simplified greatly without loss of consistency with the data. Fittings parameters are chosen to reflect the observed cosmic ray elemental hardening, softening, and two all-particle spectral features: the all-particle knee and second knee. The Matrix Cascade Equations toolkit is then utilized to calculate atmospheric muon neutrino fluxes from the fitted elemental spectra. The calculated neutrino fluxes are reported and their dependence on the underlying elemental spectra are discussed.