From detector layout to signal analysis: geometry optimization and neutron-gamma tagging in plastic scintillator detectors

Abstract

Neutrinos are elementary particles with many properties still unknown. Their masses so far have only upper and lower limits. Still, due to neutrino oscillations, it is clear that they are not massless, as stated by the Standard Model of Elementary Particles. Neutrinos are also present in the Universe in vast amounts, but they rarely interact with the surrounding matter. Their abundance makes them very interesting for many theories beyond the Standard Model, e.g., dark matter searches and charge-parity symmetry violation in the leptonic sector, which could be (partially) responsible for the observed matter-antimatter asymmetry in today’s Universe. The Deep Underground Neutrino Experiment (DUNE) is a next-generation accelerator-based neutrino oscillation experiment that will study neutrinos with unprecedented precision and may answer many open questions. DUNE uses a powerful neutrino beam from Fermilab. It consists of a Near Detector complex to measure neutrinos before oscillation, and a Far Detector complex 1300 km away to measure them after oscillation. As part of the Near Detector complex, measurements are also possible with different angles to the neutrino beam. This enables excellent control of systematic uncertainties of e.g., neutrino cross section measurements. One detector in the near detector complex is The Muon Spectrometer, an extension of a Liquid Argon detector that measures the charge and momentum of muons produced in neutrino interactions within the Liquid Argon. The design of this detector, which consists of alternating layers of steel and plastic scintillator bars, must be optimized for the expected muon energies. In this thesis, a study of the optimal module orientation plan is presented, which is necessary for the physics performance of the near detector complex and, by extension, DUNE. As part of this study, the event reconstruction was also developed and improved. Simulated muons are then reconstructed, and the performance of different module orientation plans is tested. As a second part, a study of neutron and gamma tagging using a pulse shape discrimination plastic scintillator is presented. The properties of this material allow particle differentiation based on the temporal distribution of emitted light. A novel approach to using the individual light signals was successfully tested using data from a small, local test setup.