Spectrum of cosmic-ray nucleons and the atmospheric muon charge ratio
Thomas K. Gaisser
TL;DR
This work links the TeV muon charge ratio to the composition of the primary cosmic-ray nucleons and to the forward production of π± and K± in the atmosphere by employing spectrum-weighted moments Z. It combines a three-component, rigidity-based model of the nucleon spectrum with detailed pion and kaon decay physics, including associated kaon production, to predict μ⁺/μ⁻ and νμ/ν̄μ fluxes. By comparing to multiple experimental datasets, it constrains the kaon production contribution (Z_{pK^+} ≈ 0.0079) and derives a kaon-to-pion ratio around 0.135, highlighting the non-negligible role of kaons at TeV energies. The findings have direct implications for atmospheric neutrino fluxes at high energy and demonstrate sensitivity to primary composition and forward hadroproduction.
Abstract
Interpretation of measurements of the muon charge ratio in the TeV range depends on the spectra of protons and neutrons in the primary cosmic radiation and on the inclusive cross sections for production of $π^\pm$ and $K^\pm$ in the atmosphere. Recent measurements of the spectra of cosmic-ray nuclei are used here to estimate separately the energy spectra of protons and neutrons and hence to calculate the charge separated hadronic cascade in the atmosphere. From the corresponding production spectra of $μ^+$ and $μ^-$ the $μ^+/μ^-$ ratio is calculated and compared to recent measurements. The comparison leads to a determination of the relative contribution of kaons and pions. Implications for the spectra of $ν_μ$ and $\barν_μ$ are discussed.