Abstract
To this day, no experiment has claimed to have detected a neutrino with an energy above 10 PeV, or 1016 eV. At those high energies, neutrinos are only known to be produced in the interaction of cosmic rays of even higher energies. Therefore, detecting these high-energy neutrinos can yield important clues about the most energetic regions in the universe and processes that take place in them.
The reason why the neutrinos above 10 PeV remain uninvestigated is because of their low flux, this is, the low expected rate of detection on Earth. In order to have a realistic chance at their detection, several cubic kilometres of a dense medium must be monitored for signals of neutrino interactions. One of the most recent ideas to achieve this involves the installation of a radar system in the polar ice: when the neutrino interacts with the ice, it will deposit its energy in an abrupt way, triggering a particle cascade within. The radar system is expected to be able to scatter radio waves off of this particle cascade, successfully recording the passing of a neutrino and allowing for the reconstruction of its direction and energy. This is the goal of the Radar Echo Telescope (RET) collaboration.
The goal of this thesis is to accurately model the radar scatter off of the trail left in the wake of a neutrino interaction in ice. To this end, two main efforts were conducted in this work. First, a study on the existing theory is performed to provide a consistent description of the particle cascade trail in ice. This trail is understood to be composed of the ice electrons that are freed due to ionisation processes caused by the particle cascade, and whose motion is damped due to collisions with the ice molecules. This allows for a solution of the equation of motion of the individual electrons to be found from first principles. Second, this solution is extended to the macroscopic cascade trail with the concept of the cascade’s transparency, that captures its response to the probing radar waves. Third, dedicated expressions for the radar cross section of the particle cascade and the corresponding radar range equation are constructed, which allows for a fast numerical calculation of the electric fields of the radar echo. The complete model presented in this work has been named the Macroscopic Approximation to the Radar Echo Scatter, or MARES.
Finally, a selection of results produced with the MARES model are presented. These results demonstrate the good agreement between MARES and other modelling efforts, and between MARES and the only observed radar echo from a high-energy particle cascade to date, observed at the T-576 beam test experiment at the Stanford Linear Accelerator Center (SLAC). Additionally, these results demonstrate the possibilities of the MARES model as a tool for future studies in the Radar Echo Telescope collaboration.
The reason why the neutrinos above 10 PeV remain uninvestigated is because of their low flux, this is, the low expected rate of detection on Earth. In order to have a realistic chance at their detection, several cubic kilometres of a dense medium must be monitored for signals of neutrino interactions. One of the most recent ideas to achieve this involves the installation of a radar system in the polar ice: when the neutrino interacts with the ice, it will deposit its energy in an abrupt way, triggering a particle cascade within. The radar system is expected to be able to scatter radio waves off of this particle cascade, successfully recording the passing of a neutrino and allowing for the reconstruction of its direction and energy. This is the goal of the Radar Echo Telescope (RET) collaboration.
The goal of this thesis is to accurately model the radar scatter off of the trail left in the wake of a neutrino interaction in ice. To this end, two main efforts were conducted in this work. First, a study on the existing theory is performed to provide a consistent description of the particle cascade trail in ice. This trail is understood to be composed of the ice electrons that are freed due to ionisation processes caused by the particle cascade, and whose motion is damped due to collisions with the ice molecules. This allows for a solution of the equation of motion of the individual electrons to be found from first principles. Second, this solution is extended to the macroscopic cascade trail with the concept of the cascade’s transparency, that captures its response to the probing radar waves. Third, dedicated expressions for the radar cross section of the particle cascade and the corresponding radar range equation are constructed, which allows for a fast numerical calculation of the electric fields of the radar echo. The complete model presented in this work has been named the Macroscopic Approximation to the Radar Echo Scatter, or MARES.
Finally, a selection of results produced with the MARES model are presented. These results demonstrate the good agreement between MARES and other modelling efforts, and between MARES and the only observed radar echo from a high-energy particle cascade to date, observed at the T-576 beam test experiment at the Stanford Linear Accelerator Center (SLAC). Additionally, these results demonstrate the possibilities of the MARES model as a tool for future studies in the Radar Echo Telescope collaboration.
| Original language | English |
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| Award date | 25 Jun 2024 |
| Publication status | Published - 2024 |