Development of the SHiP downstream muon detector

SHiP (Search for Hidden Particles) is a beam dump experiment proposed at CERN SPS, currently in the design stage. SHiP aims to observe long lived particles very weakly coupled with ordinary matter, as expected in a large number of Hidden Sector models, that are able do describe Dark matter, neutrino oscillation and the origins of the Barionic Asimmetry of universe. In this thesis the development of the SHiP Downstream Muon Detector is described. This subdetector aims to identify with high efficiency muons produced by signal processes and to distinguish them from neutrino- and beam-induced background ones. In order to effectively distinguish background events mistakenly reconstructed as signal vertexes due to their spatial overlapping, a time resolution better than 200 ps is mandatory. Therefore, it is extremely important that the detector components are optimized with respect to time resolution. The detector employs active layers made of plastic scintillator tiles, each coupled to silicon photomultipliers (SiPM). This thesis focuses on the development of tile prototypes that are able to meet the detector time resolution requirements, through the study of various aspects of the tile design. The improved design defined with the contribution of this thesis work has become the current baseline design and will be tested with a prototype in early 2020 at the Frascati INFN Laboratories.