Neutrino Spectrum at the Far Detector

Neutrino oscillation experiments often employ two identical detectors to minimize errors due to inadequately known neutrino beam. We examine various systematics effects related to the prediction of the neutrino spectrum in the `far' detector on the basis of the spectrum observed at the `near' detector. We propose a novel method of the derivation of the far detector spectrum. This method is less sensitive to the details of the understanding of the neutrino beam line and the hadron production spectra than the usually used `double ratio' method thus allowing to reduce the systematic errors.