theses

Neutrino physics has played a pivotal role in modern particle physics. From the postulation of its existence by Pauli in the 1930s and the introduction of neutrino oscillation phenomenology by Pontecovo in the 1950s, to the first experimental evidence of neutrino oscillations in the 1990s, the physics sector has made great strides and constantly grown, with two Nobel Prizes being awarded to related works since the turn of the century. The existence of neutrino oscillations showed that a neutrino of a given flavor has a non-zero probability of being detected after propagation as another flavor. As a result, the Pontecorvo-Maki-Nakagawa-Sakata (PMNS) matrix was developed to describe the mixing and oscillation of neutrinos between their three different flavors. Measurement of the elements of the PMNS matrix and constraining their errors have been an ongoing effort, with the ντ appearance measurement being one of them. The ANTARES detector, a megaton-volume water Cherenkov neutrino telescope located in the Mediter- ranean Sea at a depth of 2.5 kilometers, operated successfully until its decommissioning in 2022. It consisted of several hundred photomultiplier tubes (PMTs) arranged in a three-dimensional grid. Primarily designed to detect high-energy neutrinos of astrophysical origin, it was also sensitive to all neutrino flavors in the atmospheric neutrino flux with an energy threshold of a few GeV. This work focuses on tau neutrino ap- pearance, i.e. the existence of a tau neutrino atmospheric flux component resulting from neutrino flavor oscillations in the energy range of a few GeV up to 100 GeV. Using data from the full 15-year detector lifetime, an exploratory analysis was undertaken to examine the feasibility of detecting and characterizing a flux of tau neutrinos with the ANTARES detector. This is the first investigation to assess the potential sensitivity of the detector in detecting tau appearance. With a dedicated pipeline being developed to process all reconstructed data, the suitability of a reconstruction algorithm and initial cut selection criteria were identified. The calculation of the tau normalization parameter was achieved with Swim, the official tool for oscillation analysis by the Cubic Kilometre Neutrino Telescope (KM3NeT) collaboration. The sensitivities of the best-performing reconstruction algorithms have been determined when the Charged Current (CC) sector is investigated assuming Normal Mass Ordering (NMO). The results of Neural Network Fit (NNFit), the main reconstruction algorithm of this analysis, were compared with smeared versions of ”perfectly” reconstructed events, revealing that at its current level, it exhibits a sensitivity of on par with smearing 90%. The potential gains of this analysis from a better performing reconstruction algorithm have also been reviewed.

This thesis includes the radiation studies for the first nano satellite, AcubeSAT from the Aristotle University of Thessaloniki. This research was conducted inside the SpaceDot team, which participates in the third round of the "Fly Your Satel- lite!" program under of the European Space Agency(ESA). AcubeSAT is a greek student 3U-Cubesat, that host inside a biological experiment, that studies the ef- fect of radiation and microgravity to eykariotic cells, with the expected launch to occur in the second quarter of 2023. A detailed analysis for the flux and the flunce of trapped particles, solar particles and galactic cosmic rays in a LEO orbit. The LET and the total ionizing dose has been calculated for a spherical shell geometry. The simulation was conducted with the OMERE, a software developed by TRAD company with the support of CNES. In addition, two simulations methods have been performed with the FASTRAD soft- ware: the ray-tracing simulation and forward Monte Carlo simulation. Ray-tracing simulation provides a sector shielding analysis of the models, giving an overview of the received radiation dose for each specific point in the models. Forward Monte Carlo provides an overview of the deposited radiation for each section of the model, which has proven particularly useful for the state-of-the-art model, in which the deposited dosage for each part of the model has been determined. All simulations for the AcubeSAT missions indicate that the greatest contributor to radiation dose in the simulations came from trapped particles. From the dose levels results, the components of the satellite can endure and be functional during the whole duration of the mission.

This report covers the work accomplished accomplished as part of the generic elective course ΑΜΕ501 Internship of the B.S in Physics from AUTh University. The internship was performed in NCSR Democritus in the Institute of Nuclear and Particle Physics in the As- troparticle Research Group, which is a member of the KM3NeT Collaboration. The research was carried out under the guidance of Dr Ekaterini Tzamarioudaki and the invaluable help of Phd Candidate Dimitrios Stavropoulos. Data collected with the KM3NeT-ORCA detector have been used for this study. The energy resolution for reconstructed muon tracks origi- nating from neutrino interactions has been investigated. For the study an individual code, analyze_orca6_data.cc(A). Many variables were taken into consideration like the position of the vertex, the 3D direction of the incident neutrino, the energy of the neutrino and the pro- portion of the energy in the daughter particle (muon). These studies are presented in detail in the following report.