Yoichi Asaoka, Makoto Sasaki
We describe a method of observation for PeV-EeV tau neutrinos using Cherenkov light from decayed tau air shower produced by tau neutrino interactions in the earth. For observational methods utilizing earth-skimming tau neutrino events, highly precise arrival direction determination 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 uniquely developed light collectors which realize both a 42 degree-diameter field-of-view and arcminute resolution. Therefore, it has superior angular resolution in 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 signal detection produced by tau air shower. 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 its accelerators.
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http://arxiv.org/abs/1202.5656
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