Cherenkov Tau Shower Earth-Skimming Method for PeV-EeV Tau Neutrino Observation with Ashra

TL;DR

This paper presents a novel Cherenkov light detection method using the Ashra detector for observing PeV-EeV tau neutrinos via Earth-skimming air showers, emphasizing precise directionality and background estimation.

Contribution

It introduces a new Earth-skimming tau neutrino detection technique with high angular resolution using Ashra's advanced light collectors and provides detailed sensitivity and background analysis.

Findings

Ashra-1 can detect PeV-EeV tau neutrinos with high angular precision.

The method effectively distinguishes neutrino signals from cosmic-ray background.

Simulation results show promising sensitivity for neutrino astronomy.

Abstract

We describe a method of observation for PeV--EeV tau neutrinos using Cherenkov light from the air showers of decayed taus produced by tau neutrino interactions in the Earth. Aiming for the realization of neutrino astronomy utilizing the Earth-skimming tau neutrino detection technique, highly precise determination of arrival direction is key due to the following issues: (1) Clear identification of neutrinos by identifying those vertices originating within the Earth's surface; (2) Identification of very high energy neutrino sources. The Ashra detector uses newly developed light collectors which realize both a 42 degree-diameter field-of-view and arcminute resolution. Therefore, it has superior angular resolution for imaging Cherenkov air showers. In this paper, we estimate the sensitivity of and cosmic-ray background resulting from application of the Ashra-1 Cherenkov tau shower observation method. Both data from a commissioning run and a long-term observation (with fully equipped trigger system and one light collector) are presented. Our estimates are based on a detailed Monte Carlo simulation which describes all relevant shower processes from neutrino interaction to Cherenkov photon detection produced by tau air showers. In addition, the potential to determine the arrival direction of Cherenkov showers is evaluated by using the maximum likelihood method. We conclude that the Ashra-1 detector is a unique probe into detection of very high energy neutrinos and their accelerators.