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We study the advantages of a second identical detector at a medium baseline reactor neutrino experiment. A major obstruction to the determination of the neutrino mass hierarchy is the detector's unknown nonlinear energy response, which even under optimistic assumptions reduces the confidence in a hierarchy determination by about 1σ at a single detector experiment. Various energy response models are considered at one and two detector experiments with the same total target mass. A second detector at a sufficiently different baseline eliminates this 1σ reduction. Considering the unknown energy response, we find the confidence in a hierarchy determination at various candidate detector locations for JUNO and RENO 50. The best site for JUNO's near detector is under ZiLuoShan, 17 km and 66 km from the Yangjiang and Taishan reactor complexes respectively. We briefly describe other advantages, including a more precise determination of θ 12 and the possibility of a DAEδALUS inspired program to measure the CP-violating phase δ using a single pion source about 10 km from one detector and 20 km from the other. Two identical detectors provide a better energy resolution than a single detector, further increasing the confidence in a hierarchy determination.

In recent decades, inorganic crystals have been widely used in dark matter direct search experiments. To contribute to the understanding of the capabilities of CsI(Na) and CaF 2 (Eu) crystals, a mono-energetic neutron beam is utilized to study the properties of nuclear recoils, which are expected to be similar to signals of dark matter direct detection. The quenching factor of nuclear recoils in CsI(Na) and CaF 2 (Eu), as well as an improved discrimination factor between nuclear recoils and γ backgrounds in CsI(Na), are reported.