Determination of the pattern of neutrino masses at a neutrino factory

We study the precision with which the sign of delta m(32)(2) can be determined at a neutrino factory, as a function of stored muon energies and baselines. This is done by simultaneously fitting the channels nu(mu)-->nu(mu), <(nu)over bar>(e) --> <(nu)over bar>(mu) from mu(-) decays and the channels <(nu)over bar>(mu) --> <(nu)over bar>(mu), nu(e) --> nu(mu) from mu(+) decays. For a 20 GeV muon storage ring we investigate as a function of the baseline length and the magnitude of delta m(32)(2), the minimum value of the parameter sin(2)2 theta(13) for which the sign of delta m(32)(2) can be determined to at least 3 standard deviations. We find that for baselines longer than similar to 3000 km, the sign of delta m(32)(2) can be determined for sin(2)2 theta(13) down to the 10(-3) level with 10(20) decays of 20 GeV muons. (C) 2000 Elsevier Science B.V. All rights reserved.