On the Charm Contribution to the Atmospheric Neutrino Flux

TL;DR

This paper reevaluates the charm particle contribution to atmospheric neutrino flux at high energies, highlighting the significance of forward charm production and its implications for neutrino observations and cosmic neutrino flux interpretations.

Contribution

It provides new upper limits on forward charm pair production using accelerator and IceCube data, emphasizing the potential dominance of prompt flux in high-energy atmospheric neutrinos.

Findings

Prompt charm flux may dominate the high-energy atmospheric neutrino flux.

Forward charm production is significant and not well constrained by collider data.

The prompt flux cannot explain the PeV cosmic neutrino flux or IceCube's observed excess.

Abstract

We revisit the estimate of the charm particle contribution to the atmospheric neutrino flux that is expected to dominate at high energies because long-lived high-energy pions and kaons interact in the atmosphere before decaying into neutrinos. We focus on the production of forward charm particles which carry a large fraction of the momentum of the incident proton. In the case of strange particles, such a component is familiar from the abundant production of $K^{+} \Lambda$ pairs. These forward charm particles can dominate the high-energy atmospheric neutrino flux in underground experiments. Modern collider experiments have no coverage in the very large rapidity region where charm forward pair production dominates. Using archival accelerator data as well as IceCube measurements of atmospheric electron and muon neutrino fluxes, we obtain an upper limit on forward $\bar{D}^0 \Lambda_c$ pair production and on the associated flux of high-energy atmospheric neutrinos. We conclude that the prompt flux may dominate the much-studied central component and represent a significant contribution to the TeV atmospheric neutrino flux. Importantly, it cannot accommodate the PeV flux of high-energy cosmic neutrinos, nor the excess of events observed by IceCube in the 30--200 TeV energy range indicating either structure in the flux of cosmic accelerators, or a presence of more than one component in the cosmic flux observed.