The Daya Bay Reactor Neutrino Experiment has measured a non-zero value for the neutrino mixing angle $theta_{13}$ with a significance of 5.2 standard deviations. Antineutrinos from six 2.9 GW$_{rm th}$ reactors were detected in six antineutrino detectors deployed in two near (flux-weighted baseline 470 m and 576 m) and one far (1648 m) underground experimental halls. With a 43,000 ton-GW_{rm th}-day livetime exposure in 55 days, 10416 (80376) electron antineutrino candidates were detected at the far hall (near halls). The ratio of the observed to expected number of antineutrinos at the far hall is $R=0.940pm 0.011({rm stat}) pm 0.004({rm syst})$. A rate-only analysis finds $sin^22theta_{13}=0.092pm 0.016({rm stat})pm0.005({rm syst})$ in a three-neutrino framework.
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