Recherche d'un neutrino stérile avec l'expérience STEREO : développement de l'électronique et identification des neutrinos

Abstract : Since 2011, the re-evaluation of about twenty neutrino flux measurements at short distance from reactors suggests a deficit of about 7 % with respect to predictions. This anomaly has a 3 sigmas significance, as another similar anomaly which corresponds to the deficit of neutrinos emitted from intense source of beta-decay. These anomalies could be explain either by a bias in the flux prediction or by the existence of a new neutrino state, a light sterile neutrino, possibly mixing with the three neutrino states of the standard model. This new neutrino, with no ordinary weak interaction, could only be “visible” via the neutrino oscillation. The STEREO experiment goal is to answer the question of the sterile neutrino existence with mass around 1 eV, using neutrino flux emitted from the research reactor of the « Institut Laue-Langevin » (ILL) at Grenoble, France. To achieve this, the STEREO detector is segmented in 6 cells to measure a hypothetical distortion of the neutrino energy spectrum at different distances from the reactor (between 9 et 11m). Afters few years of detector construction and preparation, the STEREO experiment has started taking data in November 2016 with a first period over in Mars 2017. This thesis took place during two distinct phases of the STEREO experiment. A first part was dedicated to the characterisation and the validation of the electronics, during all its development process until its final conception. In this context, a method to measure the charge response linearity of photomultipliers and their bases, with a precision better than 1 %, has been developed, in order to fulfill the desired sensitivity to the light sterile neutrino hypothesis. This requirement on the precision has been validated by a statistical analysis of the experiment. The second part of the thesis was devoted to the analysis of the first data and more particularly to the identification of the different kinds of background and to the search of neutrino candidates.
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Thomas Salagnac. Recherche d'un neutrino stérile avec l'expérience STEREO : développement de l'électronique et identification des neutrinos. Physique des Hautes Energies - Expérience [hep-ex]. Université Grenoble Alpes, 2017. Français. ⟨NNT : 2017GREAY068⟩. ⟨tel-01757168⟩

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