| Summary: | An evaluation of the principal uncertainties in the computation of neutrino fluxes produced in cosmic ray showers in the atmosphere is presented. The neutrino flux predictions are needed for comparison with experiment to perform neutrino oscillation studies. The paper concentrates on the main limitations which are due to hadron production uncertainties. It also treats primary cosmic ray flux uncertainties, which are at a lower level. The absolute neutrino fluxes are found to have errors of around 15% in the neutrino energy region important for contained events underground. Large cancellations of these errors occur when ratios of fluxes are considered, in particular, the νμ/ν̄μ ratio below Eν=1GeV, the (νμ+ν̄μ)/(νe+ν̄e) ratio below Eν=10GeV and the up/down ratios above Eν=1GeV are at the 1% level. A detailed breakdown of the origin of these errors and cancellations is presented. © 2006 The American Physical Society.
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