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On the Charm Contribution to the Atmospheric Neutrino Flux

Francis Halzen, Logan Wille

TL;DR

The paper investigates whether forward charm production in atmospheric cosmic-ray interactions could provide a significant prompt neutrino background at high energies. It introduces a model-independent parameterization of forward charm production, constrained by ISR measurements and IceCube neutrino data, to derive an upper limit on the prompt neutrino flux from forward charm. The analysis shows that while forward charm could contribute in the 30–100 TeV range, the resulting flux cannot account for IceCube's PeV-scale cosmic neutrinos or the 30–200 TeV excess, and remains subdominant to the cosmic flux overall. The result emphasizes that forward charm is a background to consider in atmospheric-neutrino analyses but does not solve the high-energy IceCube observations.

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 $K^{+} Λ$ 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 $\bar{D}^0 Λ_c$ 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.

On the Charm Contribution to the Atmospheric Neutrino Flux

TL;DR

The paper investigates whether forward charm production in atmospheric cosmic-ray interactions could provide a significant prompt neutrino background at high energies. It introduces a model-independent parameterization of forward charm production, constrained by ISR measurements and IceCube neutrino data, to derive an upper limit on the prompt neutrino flux from forward charm. The analysis shows that while forward charm could contribute in the 30–100 TeV range, the resulting flux cannot account for IceCube's PeV-scale cosmic neutrinos or the 30–200 TeV excess, and remains subdominant to the cosmic flux overall. The result emphasizes that forward charm is a background to consider in atmospheric-neutrino analyses but does not solve the high-energy IceCube observations.

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 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 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.

Paper Structure

This paper contains 5 sections, 4 figures.

Table of Contents

  1. Introduction
  2. The Forward Charm Cross Section
  3. An Upper Limit on the Prompt Neutrino Flux
  4. Conclusions
  5. Acknowledgments

Figures (4)

  • Figure 1: The Feynman $x_F$ dependence for $\Lambda_c$ and $\bar{D}^0$ production using the parameterized cross section is compared with ISR data Bari:1991in at $\sqrt{s} = 63$ GeV.
  • Figure 2: The prompt neutrino spectrum from forward charm is shown using a baseline differential cross section and parameterizations with the $x_F$ maximum shifted up and down by 25%. The ratio of the baseline and the two shifted cross sections is also shown. Note that the break in the spectrum occurs at different energies for the shifted cross sections.
  • Figure 3: The prompt electron neutrino spectrum from forward charm is shown for extreme assumptions of the energy dependence. Also shown is the result for an intermediate dependence that exceeds the measured flux Aartsen:2015xup at the $1\,\sigma$ level at the highest energy of 20 TeV. An estimate of the contribution from centrally produced charm particles by Enberg. et al. (ERS) Enberg:2008 is shown for comparison.
  • Figure 4: The expected number of events in both the northern and southern sky for two years in IceCube using a veto-based detection scheme JVS:2014. The upper limit fluxes include the self-veto effect as prescribed in PhysRevD.90.023009. Neither upper limit can explain the high-energy events observed in IceCube.