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 determi ned at a neutrino factory, as a function of stored muon energies and baseli nes. 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(+) deca ys. For a 20 GeV muon storage ring we investigate as a function of the base line length and the magnitude of delta m(32)(2), the minimum value of the p arameter sin(2)2 theta(13) for which the sign of delta m(32)(2) can be dete rmined 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 muo ns. (C) 2000 Elsevier Science B.V. All rights reserved.