Phenomenology of the detection of ultra-high energy cosmic rays and neutrinos using the radio technique

Abstract

Ultra-high energy cosmic rays are particles that have energies up to 1020 and beyondd and that arrive to the Earth after travelling the Universe. These energies are more than one million times the energies availably by means of man-made accelerators. Cosmic rays pose several questions that remain unanswered, such as which is their composition at ultra-high energies, which are their sources (the regions of the Universe where they are produced), how they are accelerated, or how they interact with the medium while they propagate towards the Earth, etc. The existence of ultra-high energy cosmic rays that are protons or charged nuclei indicates that the production of neutrinos because of the interactions of the cosmic rays, limiting the distance the ultra-high energy cosmic rays can reach (GZK effect). On the other hand, neutrinos, being particles that interact only via weak force and with cross sections about 107 smaller than hadronic cross sections, can come from the edge of the Universe without deviating or interacting. This makes them extraordinary cosmic messengers. The detection methods of ultra-high energy cosmic rays and neutrinos involve the creation of particle showers from the interaction of the cosmic ray with a particle in a medium (atmosphere or ice, for instance). These showers are measured with detectors such as water tanks provided with photomultipliers, or fluorescence telescopes. Through the measurable quantities of a shower several properties of the initial particle can be inferred, like the energy, the type of particle, the arrival direction... One of the detection methods is the radio technique. This technique began to be developed in the 1960s, reaching some promising first results, but the limitations of the electronics at the time forced the research to stop. In the last years, and thanks to the advances in electronics, that now allows the measuring of voltages with temporal precision below the nanosecond, the radio technique is witnessing a renaissance, with experiments as ANITA, LOFAR, CODALEMA, ARA or ARIANNA. The basic idea of the radio technique is the following. When a cosmic ray or a neutrino collides with a material medium in the Earth, the resulting shower contains charged