Ultra-high energy neutrino searches and GW follow-up with the Pierre Auger Observatory

TL;DR

This paper reports on the Pierre Auger Observatory's searches for ultra-high energy neutrinos and their follow-up of gravitational wave events, setting limits on neutrino fluxes and constraining cosmic-ray models.

Contribution

It introduces the observatory's methods for detecting ultra-high energy neutrinos and presents the first follow-up of GW events with neutrino observations.

Findings

No neutrino candidates detected, leading to flux limits.

Constraints placed on cosmic-ray and neutrino production models.

Follow-up of GW events with no associated neutrino detection.

Abstract

The surface detector array (SD) of the Pierre Auger Observatory is sensitive to neutrinos at energies in the 100 PeV to 100 EeV range. This sensitivity, together with its large acceptance, makes it a complementary detector to other neutrino telescopes, which have their peak sensitivities at lower energies. The neutrino-induced air showers that the SD of the Pierre Auger Observatory is sensitive to can be divided into those induced by interactions of neutrinos of any flavor deep in the atmosphere, and those induced by charged-current interactions of tau neutrinos in the Earth's crust. Both of these types can be efficiently distinguished from cosmic ray-induced air showers, provided that their zenith angles are larger than 60{\deg}. As no neutrino candidates were found in the performed searches, we present limits on the diffuse all-flavor neutrino flux. Using these limits, we obtained constraints on cosmic-ray and neutrino production models. In the light of the recent observations of gravitational waves (GW), we also present the follow-up of LIGO/Virgo GW events. These include binary black hole merger events and also GW170817, the only binary neutron star merger ever observed directly.