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Measurement of the θ₁₃ mixing angle with the two Double Chooz detectors

Abstract : The Double Chooz experiment aims at accurately measuring the value of the leptonic mixing angle θ₁₃. To this intent, the experiment makes the most of two identical detectors -- filled with gadolinium-loaded liquid scintillator -- observing antinue's released by the two 4.25GWth nuclear reactors of the French Chooz power plant. The so-called "far detector" -- located at an average distance of 1050m from the two nuclear cores -- has been taking data since April 2011. The "near detector" -- at an average distance of 400}m from the cores -- has monitored the reactor since December 2014. The θ₁₃ mixing parameter leads to an energy dependent disappearance of antinue's as they propagate from the nuclear cores to the detection sites, which allows for a fit of the sin² 2θ₁₃ value. By reason of correlations between the detectors and an iso-flux site layout, the detection systematics and the antinue flux uncertainty on the θ₁₃ measurement are dramatically suppressed. In consequence, the precision of the θ₁₃ measurement is dominated by the uncertainty on the backgrounds and the relative normalisation of the antinue-rates. The main background originates from the decay of βn-emitters -- generated by µ-spallation -- within the detector itself. The energy spectra of these cosmogenic isotopes have been simulated and complemented by a diligent error treatment. These predictions have been successfully compared to the corresponding data spectra, extracted by means of an active veto, whose performance has been studied at both sites. The rate of cosmogenic background remaining within the antinue candidates has also been assessed. Addtionally, the normalisation of the antinue rates, bound to the number of target protons within each detector, has been evaluated. All these works were part of the first Double Chooz multi-detector results, yielding sin² (2θ₁₃) = 0.111±0.018.
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Submitted on : Monday, December 17, 2018 - 3:04:07 PM
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  • HAL Id : tel-01957696, version 1

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Valérian Sibille. Measurement of the θ₁₃ mixing angle with the two Double Chooz detectors. High Energy Physics - Experiment [hep-ex]. Université Paris Saclay (COmUE), 2016. English. ⟨NNT : 2016SACLS582⟩. ⟨tel-01957696⟩

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