The neutrino mixing angle : Reactor and accelerator experiments

Recent measurements of the neutrino mixing angle θ 13 cap a decade of observations which have clearly established the oscillation of neutrino flavor. Measurements of reactor ν ¯ e disappearance over ∼ km distances have provided a precise value for this mixing angle. Detection of ν e in beams of ν μ from particle accelerators also support a non-zero value of θ 13 , and comparisons between these two techniques are sensitive to the remaining unknowns of neutrino oscillation. The unexpectedly large value for θ 13 allows for future tests of the neutrino mass hierarchy and CP-violation in neutrino oscillation. Measurement of the energy dependence of reactor ν ¯ e disappearance has been used to determine the larger neutrino mass-squared difference, | Δ m 31 2 | ≈ | Δ m 32 2 | . Consistency with observations of accelerator ν μ disappearance supports the three-flavor model of neutrino flavor oscillation.