Internally produced events  Atmospheric neutrinos  Introduction

The atmospheric neutrino beam

Atmospheric neutrinos are produced in the pion and muon decays (kaons are important only at high energies). From these decay channels one expects at low energies about twice muon neutrinos with respect to electron neutrinos. This result doesn't change very much with a detailed calculation. There are several different calculations on the atmospheric neutrino flux. In order to compare them, we can separate the low-energy region (less than 1 GeV) from the high-energy region (more than 1 GeV). This separation corresponds to different event topologies in the detector. The low-energy region generally corresponds to events with the interaction vertex inside the detector and fully contained (peak neutrino energy around 1 GeV); the high-energy region, to events either with the interaction vertex inside the detector but not fully contained (peak neutrino energy around a few GeV) or with the interaction vertex in the rock outside the detector (peak neutrino energy around 100 GeV) ; and in the latter case only muon neutrinos can be detected. A comparison of different calculations of the atmospheric neutrino flux in the low-energy region has been made by Barr,Gaisser, Stanev (BGS). The current estimate on the error of the ratio $\nu_{e}/\nu_{\mu}$ is $\pm 5\%$. An important check for this kind of calculation comes from comparison with high-altitude muons. Several calculations also exist for the high-energy region, where the contribution due to kaon decay (50% in the energy interval between 10 GeV and 1000 GeV) is important. In the region of 10 < E $_{\nu} < 1000$ GeV, the uncertainty in the muon neutrino flux is 14%.