Antineutrinos from nuclear reactors: recent oscillation measurements

Nuclear reactors are themost intenseman-made source of antineutrinos, providing a useful tool for the study of these particles. Oscillation due to the neutrinomixing angleθ13 is revealed by the disappearance of reactor νe over∼kmdistances. Use of additional identical detectors located near nuclear reactors reduce systematic uncertainties related to reactorνe emission and detector efficiency, significantly improving the sensitivity of oscillationmeasurements. TheDouble Chooz, RENO, and Daya Bay experiments set out in search ofθ13 using these techniques. All three experiments have recently observed reactor νe disappearance, and have estimated values forθ13 of 9.3±2.1°, 9.2±0.9°, and 8.7±0.4° respectively. The energy-dependence ofνe disappearance has also allowedmeasurement of the effective neutrinomass difference, Δ ∣ ∣ mee 2 ≈ Δ ∣ ∣ m31 2 . Comparisonwith Δ ∣ ∣ μμ m 2 ≈ Δ ∣ ∣ m32 2 from accelerator νμmeasurements supports the three-flavormodel of neutrino oscillation. The current generation of reactor νe experiments are expected to reach∼3%precision in bothθ13 and Δ ∣ ∣ mee 2 . Precise knowledge of these parameters aids interpretation of plannedνμmeasurements, and allows future experiments to probe the neutrinomass hierarchy and possible CP-violation in neutrino oscillation. Absolutemeasurements of the energy spectra ofνe deviate from existingmodels of reactor emission, particularly in the range of 5–7MeV.