Neutrinos are elementary particles in the standard model of particle physics. There are 3 flavors of neutrinos that oscillate among themselves. Their oscillation can be described by a 3$times$3 unitary matrix, containing three mixing angles $theta_{12}$, $theta_{23}$, $theta_{13}$, and one CP phase. Both $theta_{12}$ and $theta_{23}$ are known from previous experiments. $theta_{13}$ was unknown just two years ago. The Daya Bay experiment gave the first definitive non-zero value in 2012. An improved measurement of the oscillation amplitude $sin^{2}2(theta_{13})$ = $0.090^{+0.008}_{-0.009}$ and the first direct measurement of the $bar u_{e}$ mass-squared difference $mid$$Delta m^2_{ee}$$mid$ = $(2.59^{+0.19}_{-0.20})times10^{-3} rm eV^{2}$ were obtained recently. The large value of $theta_{13}$ boosts the next generation of reactor antineutrino experiments designed to determine the neutrino mass hierarchy, such as JUNO and RENO-50 .
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