Hadron production uncertainties at NuMI

An improved approach for the extrapolation of the neutrino spectrum from the near to the far site is described. The method exploits the strong correlation between neutrino spectra at two arbitrary detector locations, provided that they come from the same parent hadron beam. Accuracy of the method was extensively studied on the particular example of hadron production uncertainties. Neutrino flux at the far on-axis site can be predicted more accurately than in the Far/Near ratio method. In an off-axis experiment, the integrated neutrino flux can be known to be 1-2%, even using only the on-axis near detector information. The off-axis intrinsic νe flux can be estimated to be 5% by correlating it to the νμ and ν-bar μ flux measured in an on-axis detector