The establishment of the neutrino oscillations phenomenon as a solution to both solar and atmospheric neutrino anomalies had two consequences: a new oscillation mode, labelled $mathbf{theta_{13}}$, and the possibility to observe CP violation, if $mathbf{theta_{13}}$ was sizeable. CP violation implies that neutrino oscillations behave differently for neutrinos and anti-neutrinos -- a rare fundamental phenomenon key for our understanding of the Universe. The experimental demonstration of $mathbf{theta_{13}}$ has aided the completion of a quest lasting half a century. The best $mathbf{theta_{13}}$ knowledge is today inferred from high-precision reactor neutrino disappearance. The Double Chooz (DC) experiment has played a pioneering role in this channel by providing the first positive evidence, in 2011, in combination with the T2K experiment appearance data. The establishment of $mathbf{theta_{13}}$ awaited the Daya Bay experiments observation in 2012; confirmed soon after by the RENO experiment. Todays best knowledge on $mathbf{theta_{13}}$ from reactor experiments is a key input to many neutrino experiments. Here DC reports its first multi-detector $mathbf{theta_{13}}$ measurement exploiting several unprecedented techniques for a major precision improvement.
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