Determination of the pattern of neutrino masses at a neutrino factory

We study the precision with which the sign of δm322 can be determined at a neutrino factory, as a function of stored muon energies and baselines. This is done by simultaneously fitting the channels νμ→νμ , ν̄e→ν̄μ from μ− decays and the channels ν̄μ→ν̄μ , νe→νμ from μ+ decays. For a 20 GeV muon storage ring we investigate as a function of the baseline length and the magnitude of δm322, the minimum value of the parameter sin22θ13 for which the sign of δm322 can be determined to at least 3 standard deviations. We find that for baselines longer than ∼3000 km, the sign of δm232 can be determined for sin22θ13 down to the 10−3 level with 1020 decays of 20 GeV muons.