We perform a quantitative analysis of the capability of K2K, MINOS, OPERA and a neutrino factory in a muon collider to discriminate the standard mass induced vacuum oscillation from the pure decoherence solution to the atmospheric neutrino problem and thereby contribute to unravel the dynamics that governs the observed ν µ disappearance.

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We discuss the capabilities of a future neutrino factory based on intense neutrino beams from a muon storage ring to explore the non-standard neutrino matter interactions, which are assumed to be sub-leading effects in the standard mass induced neutrino oscillations. The conjunction of these two mechanisms will magnify fake CP violating effect in the presence of matter which is not coming from the CP phase in the neutrino mixing matrix. We show that such fake CP violation can be observed in neutrino factory experiments by measuring the difference between the neutrino and anti-neutrino probabilities. In order to perform such test, we consider three neutrino flavors, admitting the mixing parameters in the range consistent with the oscillation solution to the atmospheric and the solar neutrino problems, as well as with the constraints imposed by the reactor neutrino data. We show that with a 10 kt detector with 5 years of operation, a stored muon energy E µ ≥ 20 GeV, 2 × 10 20 muon decays per year, and a baseline L ∼ 732 km, such a neutrino facility can probe the non-standard flavor changing neutrino interactions down to the level of (10 −3 − 10 −2 ) G F , in both ν µ → ν τ /ν µ →ν τ and ν e → ν τ /ν e →ν τ modes.

We discuss reactor measurement of θ 12 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 eV 2 /∆m 2 21 ], 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 sin 2 θ 12 can be determined to the accuracy of ≃ 2% (≃ 3%), at 68.27% CL for 1 degree of freedom, for 60 GW th ·kton·yr (20 GW th ·kton·yr) operation. We also discuss implications of such an accurate measurement of θ 12 .

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