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Measurement of the leptonic mixing parameter theta13 at the reactor electron antineutrino experiment Double Chooz

Vincent Durand 
Abstract : The Double Chooz experiment aims at measuring the neutrino mixing parameter theta13 by studying the oscillations of electron antineutrinos produced by the Chooz nuclear reactors located in France. The experimental concept consists in comparing the signal of two identical detectors, allowing to cancel most of the experimental systematic uncertainties. The near detector, whose goal is the flux normalization and a measurement without oscillation, is expected to be delivered in 2013. The farthest detector from the source is taking data since April 2011 and is sensitive to theta13, which is expected to affect both the rate and the shape of the measured electron antineutrinos. In this thesis, are first presented the Double Chooz experiment, with its electron antineutrinos source, its detection method, and the expected signal and backgrounds. In order to perform a selection, important quantities have to be reconstructed, calibrated, and saved in data files. The channel time offsets determination, the energy and vertex reconstruction algorithm CocoReco, the reconstruction packages of the Common Trunk, and the light trees maker Cheetah are especially presented. Concerning the data analysis, all the selection cuts and results for signal and backgrounds are discussed, particularly the multiplicity cut, the multiple offtime window method, the lithium veto cut, and the cosmogenic 9Li background studies. The Double Chooz experiment observed 8,249 electrons antineutrino candidates in 227.93 days in its far detector only. The reactor antineutrino flux prediction used the Bugey 4 flux measurement after correction for differences in core composition. The expectation in case of no-oscillation is 8,937 events and this deficit is interpreted as evidence for electron antineutrinos disappearance. From a rate and shape analysis, is found sin^2 (2theta13) = 0.109 +- 0.030 (stat) +- 0.025 (syst), with Delta m31^2 = 2.32 10^-3 eV^2, while the no-oscillation hypothesis is even excluded at 2.9 sigmas.
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Submitted on : Tuesday, November 20, 2012 - 6:07:12 PM
Last modification on : Wednesday, November 21, 2012 - 2:22:58 PM
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  • HAL Id : tel-00755262, version 1

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Vincent Durand. Measurement of the leptonic mixing parameter theta13 at the reactor electron antineutrino experiment Double Chooz. High Energy Physics - Experiment [hep-ex]. Université Paris-Diderot - Paris VII, 2012. English. ⟨NNT : ⟩. ⟨tel-00755262⟩

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