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

TL;DR

This paper assesses the uncertainties in tau lepton energy loss and neutrino cross sections at ultra-high energies, crucial for neutrino astronomy, by exploring different models of nucleon structure functions at very low x values.

Contribution

It provides a comprehensive evaluation of theoretical uncertainties in tau energy loss and neutrino cross sections at ultra-high energies using various models for nucleon structure functions.

Findings

Uncertainty factor of 4 in tau energy loss at 10^9 GeV.

Uncertainty factor of 2 in neutrino cross section at 10^9 GeV.

Nuclear shadowing and saturation effects could be stronger than current models suggest.

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.