The neutrino mixing angle θ13θ13: Reactor and accelerator experiments

Recent measurements of the neutrino mixing angle θ13θ13 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 νeνe in beams of νμνμ from particle accelerators also support a non-zero value of θ13θ13, and comparisons between these two techniques are sensitive to the remaining unknowns of neutrino oscillation. The unexpectedly large value for θ13θ13 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, |Δm312|≈|Δm322|. Consistency with observations of accelerator νμνμ disappearance supports the three-flavor model of neutrino flavor oscillation.