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Blanchet, Adrien
Universite de Paris-Sud, 15 rue Georges Clemenceau - 91405 Orsay cedex (France); Universite de Paris-Saclay, Espace Technologique, Immeuble Discovery, Route de l'Orme aux Merisiers RD 128, 91190 Saint-Aubin, (France); CEA, DRF-IRFU (France)2019
Universite de Paris-Sud, 15 rue Georges Clemenceau - 91405 Orsay cedex (France); Universite de Paris-Saclay, Espace Technologique, Immeuble Discovery, Route de l'Orme aux Merisiers RD 128, 91190 Saint-Aubin, (France); CEA, DRF-IRFU (France)2019
AbstractAbstract
[en] The doctoral thesis focuses on the physics of reactor neutrinos. The increasingly precise study of antineutrinos spectra from reactors has revealed a deviation between the prediction and the measurements, which could indicate the existence of a new neutrino. This new neutrino state would not couple with the weak interaction (a sterile neutrino) and its mass would be around 1 eV/c2. The STEREO experiment aims at testing the sterile neutrino hypothesis at the ILL reactor in Grenoble-France. The principle of the STEREO experiment is based on 6 identical detector cells aligned between 9 and 11.5 m distance from the core of the ILL research reactor. The detector started taking data in November 2016, and the first results were published in 2018. The work carried out during the thesis initially consisted in characterizing the detector's energy response. During the first phase of data taking, hardware failures occurred leading to the optical decoupling of a cell and a gradual increase in light cross-talk between cells. These two aspects have compelled data analysis to develop a dedicated energy deposit reconstruction algorithm that corrects first-order light leaks using a matrix formalism. Significant work on the measurement of the parameters of this method was undertaken to ensure that the energy scale was well reproduced in the GEANT4 simulation. The estimation of systematic uncertainties on the energy scale was performed using cosmogenic background events. The second major aspect addressed during the thesis is the statistical analysis and generation of exclusion contours of the sterile neutrino hypothesis. The statistical inference was built using the Feldman and Cousins (1999) method by generating frequentist confidence intervals. A formalization in X2 has been specially developed to conduct the oscillation analysis independently of any flux or shape prediction of the antineutrino spectra. Statistical and systematic errors were propagated using covariance matrices and X2 laws were constructed by generating pseudo-experiments. All the work carried out during this doctoral thesis contributed to the publication of three papers presenting the results of the STEREO experiment. (author)
[fr]
La these de doctorat porte sur la physique des neutrinos de reacteurs. L'etude de plus en plus precise des spectres d'antineutrinos des reacteurs a mis a jour une deviation entre la prediction et les mesures qui pourrait indiquer l'existence d'un nouveau neutrino, non couple avec l'interaction faible (un neutrino sterile) et de masse autour de 1 eV/c2. L'experience STEREO vise a tester l'hypothese du neutrino sterile aupres du reacteur ILL de Grenoble. Le principe de STEREO repose sur 6 cellules de detection identiques disposees entre 9 et 11.5 m de distance du coeur du reacteur de recherche de l'ILL. Le detecteur a commence la prise de donnees en novembre 2016, et les premiers resultats ont ete publies des 2018. Le travail effectue pendant la these a consiste dans un premier temps a caracteriser la reponse en energie du detecteur. Pendant la premiere phase de prise de donnees, des defaillances materielles se sont manifestees entrainant le decouplage optique d'une cellule et une augmentation progressive des fuites de lumiere entre cellules. Ces deux aspects ont contraint l'analyse de donnees a developper un algorithme de reconstruction des depots d'energie qui corrige les fuites lumieres au premier ordre. Un important travail sur la mesure des parametres de cette methode a ete entrepris afin d'assurer que l'echelle en energie soit bien reproduite dans la simulation GEANT4. L'estimation des incertitudes systematiques sur l'echelle en energie a ete effectuee en se servant des bruits de fond cosmogeniques. Le second aspect majeur aborde pendant la these est l'analyse statistique et la generation des contours d'exclusion de l'hypothese du neutrino sterile. La deduction statistique a ete conduite en s'inspirant de la methode de Feldman et Cousins (1999) sur la generation d'intervalles de confiance frequentistes. Un formalise en X2 a specialement ete developpe pour mener une analyse d'oscillations independante des predictions de flux et de forme des spectres antineutrinos. Les erreurs statistiques et systematiques ont ete propagees a l'aide de matrices de covariance et les lois de X2 ont ete calculees en generant des pseudo-experiences. L'ensemble des travaux menes pendant cette these de doctorat a contribue a la publication de trois papiers presentant les resultats de l'experience STEREOOriginal Title
Recherche du neutrino sterile aupres du reacteur de l'ILL: experience Stereo
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3 Oct 2019; 233 p; 221 refs.; Available from the INIS Liaison Officer for France, see the INIS website for current contact and E-mail addresses; Physique des Particules
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Report
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