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Reactor measurement of θ<inf>12</inf>: Principles, accuracies, and physics potentials

Abstract:

We discuss reactor measurement of θ12 which has a potential of reaching the ultimate sensitivity which surpasses all the methods so far proposed. The key is to place a detector at an appropriate baseline distance from the reactor neutrino source to have an oscillation maximum at around a peak energy of the event spectrum in the absence of oscillation. By a detailed statistical analysis the optimal distance is estimated to be ≃ (50 - 70) km × [8 × 10-5 eV2/Δm 212], which is determined by maximizing the oscillation effect in the event number distribution and minimizing geo-neutrino background contamination. To estimate possible uncertainty caused by surrounding nuclear reactors in distance of ∼100 km, we examine a concrete example of a detector located at Mt. Komagatake, 54 km away from the Kashiwazaki-Kariwa nuclear power plant in Japan, the most powerful reactor complex in the world. The effect turns out to be small. Under a reasonable assumption of systematic error of 4% in the experiment, we find that sin2θ12 can be determined to the accuracy of ≃ 2%(≃ 3%), at 68.27% CL for 1 degree of freedom, for 60 GWth · kton · yr (20 GWth · kton · yr) operation. We also discuss implications of such an accurate measurement of θ12. © 2005 The American Physical Society.