Daya Bay experiment measures final neutrino mixing angle

Science : At a seminar today at the Institute of High Energy Physics of the Chinese Academy of Sciences in Beijing, the team behind the Daya Bay Neutrino Experiment presented the results of its campaign to measure θ ₁₃, one of three so-called mixing angles that characterize how the three neutrino flavors—electron, muon, and tau—transform into each other. The other two mixing angles, θ ₁₂ and θ ₂₃, had already been determined. At 8.8°, the value of θ ₁₃ is significantly larger than zero and therefore brings relief to theorists who are striving to explain why the universe contains more matter than antimatter. The source of that asymmetry now appears to lie in the properties and interactions of neutrinos. The Daya Bay Neutrino Experiment is a huge undertaking. Three geographically separated pairs of gigawatt nuclear reactors in China’s Guangdong province produce antineutrinos that are detected in three underground halls nearly 2 kilometers apart. Designed to measure values of θ ₁₃ as low as 0.1°, the experiment needed just 55 days to yield a statistically significant result.