Limits on the flux of tau neutrinos from 1 PeV to 3 EeV with the MAGIC telescopes

TL;DR

This paper reports on the search for tau neutrino-induced air showers using the MAGIC telescopes, setting upper limits on neutrino fluxes in the PeV to EeV range based on observational data and simulations.

Contribution

It introduces a method to discriminate tau neutrino signals from background using Monte Carlo simulations and provides new flux limits based on MAGIC telescope observations.

Findings

Set a 90% C.L. limit of $E_{ u_{ au}}^{2}\times \phi (E_{ u_{\tau}}) < 2.0 \times 10^{-4}$ GeV cm$^{-2}$ s$^{-1}$ for 1 PeV to 3 EeV.

Projected limits with 300 hours of data could reach $8.4 \times 10^{-6}$ GeV cm$^{-2}$ s$^{-1}$ under optimistic conditions.

Demonstrated the feasibility of using Cherenkov telescopes for tau neutrino detection.

Abstract

A search for tau neutrino induced showers with the MAGIC telescopes is presented. The MAGIC telescopes located at an altitude of 2200 m a.s.l. in the Canary Island of La Palma, can point towards the horizon or a few degrees below across an azimuthal range of about 80 degrees. This provides a possibility to search for air showers induced by tau leptons arising from interactions of tau neutrinos in the Earth crust or the surrounding ocean. In this paper we show how such air showers can be discriminated from the background of very inclined hadronic showers by using Monte Carlo simulations. Taking into account the orography of the site, the point source acceptance and the event rates expected have been calculated for a sample of generic neutrino fluxes from photo-hadronic interactions in AGNs. The analysis of about 30 hours of data taken towards the sealeads to a 90\% C.L. point source limit for tau neutrinos in the energy range from $1.0 \times 10^{15}$ eV to $3.0 \times 10^{18}$ eV of about $E_{\nu_{\tau}}^{2}\times \phi (E_{\nu_{\tau}}) < 2.0 \times 10^{-4}$ GeV cm$^{-2}$ s$^{-1}$ for an assumed power-law neutrino spectrum with spectral index $\gamma$=-2. However, with 300 hours and in case of an optimistic neutrino flare model, limits of the level down to $E_{\nu_{\tau}}^{2}\times \phi (E_{\nu_{\tau}}) < 8.4 \times 10^{-6}$ GeV cm$^{-2}$ s$^{-1}$ can be expected.