# Probing the origin of ultra-high-energy cosmic rays with neutrinos in the EeV energy range using the Pierre Auger Observatory

## TL;DR

This study used 14.7 years of Pierre Auger Observatory data to search for ultra-high-energy neutrinos, setting strict upper limits on their flux and constraining models of cosmic ray sources.

## Contribution

First comprehensive search for EeV neutrinos with the Pierre Auger Observatory, establishing new upper bounds on their flux and impacting models of cosmic ray origins.

## Key findings

- No neutrino candidates detected in 14.7 years.
- Set a 90% CL upper limit on neutrino flux at $E^2 dN/dE < 4.4 imes 10^{-9}$ GeV cm$^{-2}$ s$^{-1}$ sr$^{-1}$.
- Strongly constrains models of neutrino production and cosmic ray sources.

## Abstract

Neutrinos with energies above $10^{17}$ eV are detectable with the Surface Detector Array of the Pierre Auger Observatory. The identification is efficiently performed for neutrinos of all flavors interacting in the atmosphere at large zenith angles, as well as for Earth-skimming $\tau$ neutrinos with nearly tangential trajectories relative to the earth. No neutrino candidates were found in $\sim\,14.7$ years of data taken up to 31 August 2018. This leads to restrictive upper bounds on their flux. The $90\%$ C.L. single-flavor limit to the diffuse flux of ultra-high-energy neutrinos with an $E_\nu^{-2}$ spectrum in the energy range $1.0 \times 10^{17}~{\rm eV} - 2.5 \times 10^{19}~{\rm eV}$ is $E^2 {\rm d}N_\nu/{\rm d}E_\nu < 4.4 \times 10^{-9}~{\rm GeV~cm^{-2}~s^{-1}~sr^{-1}}$, placing strong constraints on several models of neutrino production at EeV energies and on the properties of the sources of ultra-high-energy cosmic rays.