Daya Bay's first results were announced in March 2012 and established the unexpectedly large value of the mixing angle theta one-three, the last of three long-sought neutrino mixing angles. The new results from Daya Bay put the precise number for that mixing angle at sin2θ)=0.090 plus or minus 0.009.. . .From (this press release.
From the KamLAND experiment in Japan, they already know that the difference, or "split," between two of the three mass states is small. They believe, based on the MINOS experiment at Fermilab, that the third state is at least five times smaller or five times larger. Daya Bay scientists have now measured the magnitude of that mass splitting, |Δmee|, to be (2.59±0.20)x10 eV. The result establishes that the electron neutrino has all three mass states and is consistent with that from muon neutrinos measured by MINOS. Precision measurement of the energy dependence should further the goal of establishing a "hierarchy," or ranking, of the three mass states for each neutrino flavor.
MINOS, and the Super-K and T2K experiments in Japan, have previously determined the complementary effective mass splitting (Δm μμ) using muon neutrinos. Precise measurement of these two effective mass splittings would allow calculations of the two mass-squared differences (Δm 32 and Δm 31) among the three mass states. KamLAND and solar neutrino experiments have previously measured the mass-squared difference Δm 21 by observing the disappearance of electron antineutrinos from reactors about 100 miles from the detector and the disappearance of neutrinos from the sun.
Neither of the two numbers is far from previous estimates. As of March 2012, the estimates were sin2(2θ13) = 0.092±0.017 and |Δm231| ≈ |Δm232| ≡ Δm2 atm = 2.43+0.13−0.13×10−3 eV2.
The precision in the theta13 number is about twice as great as the estimate from a year and a half ago, and is slightly lower than previously estimated. But, the results are consistent with each other at the one sigma level. The mass splitting estimate is consistent with prior data and similar in precision on a percentage basis.