# Determining the fraction of cosmic-ray protons at ultra-high energies with cosmogenic neutrinos

## TL;DR

This paper explores how measurements of cosmogenic neutrinos can indirectly determine the proportion of protons among ultra-high-energy cosmic rays, offering a model-independent way to understand their composition and source origins.

## Contribution

It demonstrates the current constraints from neutrino observations on the proton fraction in UHECRs and discusses future detector prospects for improved constraints.

## Key findings

- Current neutrino limits already restrict proton fractions in UHECRs.
- Next-generation detectors will significantly improve these constraints.
- Implications for various UHECR source models are analyzed.

## Abstract

Cosmogenic neutrinos are produced when ultra-high-energy cosmic rays (UHECRs) interact with cosmological photon fields. Limits on the diffuse flux of these neutrinos can be used to constrain the fraction of protons arriving at Earth with energies $E_{p} \gtrsim 30$ EeV, thereby providing constraints on the composition of UHECRs without fully relying on hadronic interaction models. We show to which extent current neutrino telescopes already constrain this fraction of protons and discuss the prospects for next-generation detectors to further constrain it. Additionally, we discuss the implications of these limits for several popular candidates for UHECR source classes.