The role of charm and unflavored mesons in prompt atmospheric lepton fluxes

TL;DR

This paper evaluates how charm and unflavored mesons influence prompt atmospheric lepton fluxes, highlighting the impact of intrinsic charm in cosmic ray interactions and the challenges in reconciling model predictions with IceCube measurements.

Contribution

It introduces new models of intrinsic charm in cosmic ray interactions and assesses their effects on atmospheric lepton flux predictions, addressing discrepancies with IceCube data.

Findings

Intrinsic charm increases prompt muon and neutrino fluxes.

Scaling unflavored meson contributions can reconcile models with observations.

Current models face tensions with IceCube's muon and neutrino flux measurements.

Abstract

The all-sky very-high-energy ($10^4-10^6$ GeV) atmospheric muon flux measured by IceCube shows a spectral hardening at the highest energies, indicating the presence of a prompt component. IceCube has also measured the atmospheric muon neutrino flux at high energy. However, since this flux is dominated by astrophysical neutrinos, only an upper bound can be placed on the prompt atmospheric $\nu_\mu+\bar{\nu}_\mu$ contribution. In this work, we provide a new evaluation of the prompt atmospheric muon flux including an intrinsic charm component in the cosmic ray-air interactions. The latter enhances the forward production of $\bar{D}^0$, $D^-$, and $\Lambda_c$, which subsequently decay into final states containing muons and muon neutrinos. We show how the increase in the prompt muon flux due to intrinsic charm is accompanied by a corresponding enhancement in the prompt muon neutrino flux. We implement different intrinsic charm production models in \texttt{MCEq} to calculate the resulting lepton fluxes. We discuss the challenges of achieving predictions that are simultaneously consistent with both IceCube's high-energy atmospheric muon flux measurements and IceCube upper bounds on the prompt muon neutrino flux, and we quantify the resulting discrepancies. As possible solutions, we explore scaling of the unflavored meson contributions to the prompt atmospheric muon flux to assess how such adjustments can reconcile these differences. The tensions emphasized in our work call for a refinement of the hadronic interaction models, especially the production of unflavored mesons, and for new experimental data sensitive to unflavored meson and heavy flavor production with reliable estimates of the associated uncertainties. We suggest that the energy and zenith angle dependence of muon and neutrino flux ratios from future neutrino telescope measurements may help to disentangle different scenarios.