Non-Standard Interactions: Atmospheric versus Neutrino Factory Experiments

We consider the potential of a generic neutrino factory (NUFACT) in probing non-standard neutrino-matter interactions (NSI). We find that the sensitivity to flavour-changing (FC) NSI can be substantially improved with respect to present atmospheric neutrino data, especially at energies higher than approximately 50 GeV, where the effect of the tau mass is small. For example, a 100 GeV NUFACT can probe FC neutrino interactions at the level of few $|\epsilon| < {few} \times 10^{-4}$ at 99 % C.L.