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Medium Baseline Reactor Neutrino Experiments with 2 Identical Detectors

In the next 10 years medium baseline reactor neutrino experiments will attempt to determine the neutrino mass hierarchy and to precisely measure θ_12. Both of these determinations will be more reliable if data from identical detectors at distinct baselines are combined. While interference effects can be eliminated by choosing detector sites orthogonal to the reactor arrays, one of the greatest challenges facing a determination of the mass hierarchy is the detector's unknown energy response. By comparing peaks at similar energies at two identical detectors at distinct baselines, one eliminates any correlated dependence upon a monotonic energy response. In addition, a second detector leads to new hierarchy-dependent observables, such as the ratio of the locations of the maxima of the Fourier cosine transforms. Simultaneously, one may determine the hierarchy by comparing the χ^2 best fits of ΔM^2_32 at the two detectors using the spectra associated to both hierarchies. A second detector at a distinct baseline also breaks the degeneracy between θ_12 and the background neutrino flux from, for example, distant reactors and increases the effective target mass, which is limited by current designs to about 20 kton/detector.