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Title
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Search for sterile neutrinos in the eV and MeV mass range with the SoLid detector
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Author
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Abstract
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| The discovery of neutrino oscillations exposed the need for physics beyond the Standard Model. The neutrinos' behavior could be explained with additional neutrino states. Several anomalies in neutrino experiments gave rise to the hypothesis of a new sterile neutrino mass state with Δm² ~ 1 eV². The SoLid experiment will investigate flavor oscillations to the new state by measuring the dependence of the νe flux to a distance -and energy range, with a 1.6 ton, highly segmented detector at very short baseline of 6-9 m from the compact core of the 60 MW BR2 reactor of the Belgian Nuclear Research Center SCK-CEN. In addition, we will investigate the sensitivity of the SoLid detector to probe heavier sterile neutrinos (HNL) in the mass range of 1-10 MeV, by detecting their decay products. To perform the challenging measurements in a high radiation environment - close to the nuclear reactor and at Earth's surface - an innovative hybrid scintillator technology was developed, combining polyvinyltoluene and 6LiF:ZnS(Ag) scintillators into a unit cell of 5 × 5 × 5 cm³ to reach the necessary particle identification and energy reconstruction. 12800 of these unit cells make up the detector, which is read by a network of fibers and MPPCs. To validate the detector operation and to understand and predict the neutrino signal and the various background sources, a simulation framework was established. The present thesis describes how the simulation of the detector readout is developed and fine-tuned. The simulation models the energy response of the detector, converting energy deposits of passing particles to data-like output signals. This covers the photon generation and transport, the sensor response, the construction of digital waveform signals, the trigger operation and the signal readout with zero suppression. The implemented models are based on calibration measurements, detector data taken during reactor on and off periods, dedicated testbenches and specifications from manufacturers. The simulated neutrino and background events are used to construct selection requirements and train the Machine Learning models. For the oscillation analysis, a signal excess of 90 ± 22.8 IBD events per day can be reached, with a signal-to-background ratio of 1:5. The full oscillation analysis is expected this year. For the HNL analysis, the sensitivity study indicates that we have the potential to set stricter exclusion limits on the HNL parameter space in the low mass range than the previous lab experiments, namely Bugey and Triumf. |
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Language
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English
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Publication
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Antwerp
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University of Antwerp, Particle Physics Group
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2021
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Volume/pages
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312 p.
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Note
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Van Remortel, Nick [Supervisor]
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Full text (open access)
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