Neutrinos could play an important role in connecting several branches of particle astrophysics. The origin of ultra high energy cosmic ray (UHECR) is still a great puzzle. Bottom-up theories propose that they originate from energetic process such as Active Galactic Nuclei (AGN) or Gamma Ray Bursts (GRB). On the other hand, top-down theories suggest that UHECR are decay products of
topological defects or heavy relic particles. Measurement of neutrino flux at and above the knee region (ie. $>10^{15}$ eV) provides a good discriminator to distinguish between the two scenarios.

However, because of the extremely low flux (energy $>10^{15}$ eV) and small interaction cross section, conventional neutrino telescopes need detection volume in the order of km. Limited by dimension of detector volume, these detectors are sensitive at energy $<10^{15}$ eV. Ultra high energy cosmic ray detectors could detect
neutrinos at energy above $10^{18}$ eV.

The gap from $10^{15}$ to $10^{18}$ eV can be filled by our proposed neutrino telescope (NuTel). Using the earth or mountain as the target for converting neutrinos
into leptons, we can detect the air shower initiated from the these leptons. Our goal is using the Monte-Carlo method to simulate the sensitivity of NuTel.

First, we simulate the reaction of neu-tau in mountain. By considering the charge-current and neutral-current interactions, we can get the conversion rate of neu-tau to tau-lepton and the distribution function of the out-going tau energy. Second, we use the GIS terrain data to simulate some selected sites. Considering the tau decay length, Cherenkov light produced by air shower and adding
the threshold of photon numbers of our telescope, we can get the acceptance. With the event rate 0.3/year/half decade of energy, we can estimate the sensitivity. Finally, we will make a comparison between different sites and between our NUTEL and other similar experiments.

Chapter1 Introduction page 1
1.1 Neutrino Physics page 1
1.2 Ultra High Energy Neutrino Astronomy page 2
1.3 Neutrino Telescope--Earth-Skimming Technique page 3
Chapter2 The process of Tau-Neutrinos to Tau-leptons in terra page 7
2.1 Monte-Carlo Method page 7
2.2 Tau Decay, Energy Loss and Tau Range page 8
2.3 The process of Tau-Neutrinos to Tau-Leptons page13
Chapter3 Acceptance and Sensitivity of some potential sites page19
3.1 Simulation Method page19
3.2 Conditions of Potential Sites page23
3.3 Simulation Results page26
Chapter4 Conclusion page33

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