Toward the search of a sterile neutrino with the SoLid experiment at the SCK-CEN BR2 reactor: detector calibration and design of a multivariate topological selection of antineutrino events

The SoLid experience is based near the BR2 research reactor at SCK-CEN, Belgium. Its aim is to search for neutrino oscillation at very short baseline, which would explain the so-called Reactor Antineutrino Anomaly via the presence of a new particle, a sterile neutrino. The measurement of antineutrino energy spectrum from the reactor highly enriched in Uranium 235, SoLid would help to understand the disagreement between predicted and measured observed by previous experiment (so-called 5 MeV bump). In order to fight against the important cosmic induced background inherent in ground-level experiment, the SoLid detector is high segmented: with 12,800 detection cells read-out by 3,200 MPPCs. Electronic antineutrinos are detected via Inverse Beta Decay (IBD), thanks to a new detection technology involving the combination of plastic scintillator, the PVT, and mineral scintillator, the ZNS. Thesis contributions could divided in three main parts. First consisted in the energy calibration of the detector. This is a challenge due to the high segmentation of the target. The second one extended the calibration by adjusting the energy response in the simulation improved its code. Finally, the last one conceived the selection and extraction of the signal. With the development of new discriminating variables which exploits the annihilation gammas from IBD and using multivariate analysis tools. Then via the improvement of the official signal extraction method and the development of a new one for comparison purpose. Among other things, my work allows to control the energy scale of SoLid cubes at around a 2% level and improve by a factor 4 the signal over background ratio for the same signal efficiency. (author)