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Measurement of the electron-antineutrino angular correlation coefficient a in neutron β-decay with the spectrometer aSPECT

Lundi 17 février 2014 11:00 - Duree : 1 heure
Lieu : Seminar room ILL1, 6 rue Jules Horowitz - Grenoble

Orateur : R. MAISONOBE (ILL)

Neutron β-decay is parametrized by several measurable correlation coefficients, which are used to determine parameters of the Standard Model and to search for new physics. The aim of the retardation spectrometer aSPECT is to measure the electron-antineutrino angular correlation coefficient a with an unprecedented accuracy of well below 1%. The coefficient is extracted from a high precision measurement of the proton energy spectrum. A central point of this PhD thesis is the analysis of the background, motivated by the observations of discharges during the beam time of 2011, and an earlier indication for a dependence on the retardation potential. During this thesis, several measurements were conducted off-line, without ionizing particles from neutron decay. An “internal” background (X-rays and ions) was identified. It has an influence of 10-5-10-4 on Δa/a depending on the vacuum level (around 10-9 mbar) and the spectrometer settings. Within the analysis of the data from the beam time in 2013, a model was built to correct for backgrounds present in the neutron decay experiment, taking into account its time dependence. The correction is about 3% on the coefficient for standard settings and vacuum but it can reach 7% for unfavorable settings. To reduce the background, a drift electric field was applied close to the maximum of the retardation potential. Additional measurements performed during this beam time included tests of systematics, in particular the edge effect (beam profile) and different electrode settings. In order to obtain the final result, the analysis has to be extended by including the different corrections and by comparing with simulations of the systematic effects.

Contact : blanc@ill.fr

Discipline évènement : (Physique)
Entité organisatrice : (ILL)
Nature évènement : (Séminaire)
Evènement répétitif : (General ILL Seminar - College 3)
Site de l'évènement : Polygone scientifique

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