Determining Neutrino Mass Hierarchy by Precision Measurements in Electron and Muon Neutrino Disappearance Experiments

Abstract

Recently a new method for determining the neutrino mass hierarchy by comparing the effective values of the atmospheric Δm^2 measured in the electron neutrino disappearance channel, Δm^2(ee), with the one measured in the muon neutrino disappearance channel, Δm^2(μμ), was proposed. If Δm^2(ee) is larger (smaller) than Δm^2(μμ) the hierarchy is of the normal (inverted) type. We re-examine this proposition in the light of two very high precision measurements: Δm^2(μμ) that may be accomplished by the phase II of the Tokai-to-Kamioka (T2K) experiment, for example, and Δm^2(ee) that can be envisaged using the novel Mossbauer enhanced resonant \barν_e absorption technique. Under optimistic assumptions for the systematic uncertainties of both measurements, we estimate the parameter region of (θ_13, δ) in which the mass hierarchy can be determined. If θ_13 is relatively large, sin^2 2θ_13 \gsim 0.05, and both of Δm^2(ee) and Δm^2(μμ) can be measured with the precision of \sim 0.5 % it is possible to determine the neutrino mass hierarchy at > 95% CL for 0.3 π\lsim δ\lsim 1.7 πfor the current best fit values of all the other oscillation parameters.