Charged Current Neutrino Cross Section and Tau Energy Loss at Ultra-High Energies

TL;DR

This paper assesses the theoretical uncertainties in two crucial quantities for Earth-skimming tau neutrinos at ultra-high energies: the tau energy loss from photonuclear interactions and the charged current neutrino-nucleus cross section. By employing a range of structure-function models and extrapolation schemes to extremely low x and varying Q^2, including saturation-based approaches, the authors quantify uncertainty bands and reveal strong model dependence. They find that tau energy loss can vary by up to a factor of ~4 at E ~ 10^9 GeV, while the CC cross section varies by about a factor of 2, with saturation effects generally reducing etc. The work emphasizes the need for consistent use of structure functions across both processes to robustly interpret Earth-skimming neutrino bounds and informs the design and analysis of high-energy neutrino detectors.

Abstract

We evaluate both the tau lepton energy loss produced by photonuclear interactions and the neutrino charged current cross section at ultra-high energies, relevant to neutrino bounds with Earth-skimming tau neutrinos, using different theoretical and phenomenological models for nucleon and nucleus structure functions. The theoretical uncertainty is estimated by taking different extrapolations of the structure function F2 to very low values of x, in the low and moderate Q2 range for the tau lepton interaction and at high Q2 for the neutrino-nucleus inelastic cross section. It is at these extremely low values of x where nuclear shadowing and parton saturation effects are unknown and could be stronger than usually considered. For tau and neutrino energies E=10^9 GeV we find uncertainties of a factor 4 for the tau energy loss and of a factor 2 for the charged current neutrino-nucleus cross section.

Figures (11)

• Figure 1: The proton structure function $F_2$ as a function of $x$ for different high $Q^2$(GeV$^2$) values. Data points are from HERA H1DATAZEUSDATA.
• Figure 2: The proton structure function $F_2$ as a function of $x$ for different low $Q^2$ (GeV$^2$) values. Data points are from HERA H1DATAZEUSDATA.
• Figure 3: The nuclear correction factor $f^A$ as a function of $x$.
• Figure 4: The photonuclear energy loss rate, $b(E)$, computed in different models.
• Figure 5: The effect of nuclear corrections on the photonuclear energy loss rate, $b(E)$.