Search for the origin of cosmic rays with the antares neutrino telescope
- Autores: Sergio Alves Garre
- Directores de la Tesis: Francisco Salesa Greus (dir. tes.), Agustín Sánchez Losa (codir. tes.)
- Lectura: En la Universitat de València ( España ) en 2025
- Idioma: español
- Tribunal Calificador de la Tesis: Antoine Kouchner (presid.), Juan Antonio Aguilar Sánchez (secret.), Giulia Illuminati (voc.)
- Programa de doctorado: Programa de Doctorado en Física por la Universitat de València (Estudi General)
- Materias:
- Enlaces
- Tesis en acceso abierto en: TESEO
- Resumen
The origin of cosmic rays, particularly those with the highest energies, remains one of the unresolved questions in modern physics. The cosmic-ray flux that arrives at Earth is mostly composed of protons and heavier nuclei and reaches energies a million times larger than those achieved in man-made accelerators. Understanding how and where those protons and heavy nuclei are accelerated to TeV and higher energies has been among the most important topics of research of the astroparticle physics community for a long time. This question is also tightly connected to the origins of non-thermal electromagnetic emissions from certain sources which correspond to those expected from particles that are being accelerated inside them. These particles would mainly be electrons and protons yet, for many of the known potential sources, the observed gamma-ray spectrum could be well explained with electron acceleration only.
However, since hadronic models predict gamma-rays from the decay of neutral pions produced in the interaction of the protons with the medium, high energy neutrinos from the decay chain of charged pions are also expected. Neutrinos would be able to escape from the source and travel long distances without being absorbed. As they have no charge they would not be deflected by magnetic fields on their way pointing back straight to their production site. Hence, high energy astrophysical neutrinos not only allow for an unambiguous identification of hadronic processes taking place, but also for the identification of individual sources.
Cherenkov neutrino telescope detection principle is based on detecting the Cherenkov light emitted by the particles produced in the interaction of the neutrino with the detection medium. Hence, neutrino telescopes are built as arrays of light detecting elements. The ANTARES detector was a water Cherenkov neutrino telescope located 2500 m deep in the Mediterranean Sea, 40 km away from the coast of Toulon, which operated from 2007 until the beginning of 2022. ANTARES was composed of 12 vertical lines that were deployed ~70 m from each other following an octagonal pattern. Each line hosted 25 storeys equipped with three photomultiplier tubes, each one shielded by a pressure-resistant glass sphere called optical module. The vertical distance between storeys was 14.5 m. The total instrumented volume of ANTARES was 0.01 km3 with a total of 885 optical modules. Each line was also equipped with five hydrophones and four optical beacons for acoustic positioning and time calibration purposes respectively. Due to the optical properties of the water in the detector site, ANTARES could detect neutrinos with sub-degree angular resolution.
Still, Cherenkov neutrino telescopes such as ANTARES are dominated by atmospheric backgrounds: muons coming from the down-going direction and atmospheric neutrinos interacting near the detector coming from every direction, consequence of the interaction of cosmic-rays with the higher layer of the atmosphere. The muon component can be efficiently removed by limiting your search to events coming through the Earth, while the atmospheric neutrinos can only be handled via statistical analyses sensitive to event energy spectra and clustering. Since ANTARES was located in the Northern Earth Hemisphere, it had a great view of neutrinos coming from the Southern Sky, where the main part of the Galactic Plane lies, including the Galactic Centre.
In this work we search for point-like and extended high-energy neutrino sources. We expect this cosmic signal to dominate at higher energies (E >10 TeV) while atmospheric neutrinos do it at lower values. Additionally, while the atmospheric background is distributed homogeneously over all directions, cosmic neutrino signal is expected to cluster around the direction of the sources over the atmospheric background. This information is used by a likelihood function to estimate the cosmic and atmospheric components of our data and at which level of confidence.
Using the likelihood formalism, three different searches are proposed. First, the fullsky searches for high-energy neutrino clusters. This approach can unveil unknown sources but with low significance. Second, a list of known potential candidates is explored. Finally, the Galactic Plane is surveyed for potential neutrino emission as in the fullsky analysis, but assuming that the source has also an unknown extension. No evidence of neutrino emission was found in any of the three searches so upper limits on the neutrino flux were set.
Time-dependent neutrino emission from some sources is also tested using the likelihood formalism and a "cut and count" strategy. These analyses benefit from considering information on the expected arrival time of neutrinos enhancing the detection performance. Still, no neutrinos signal was found and limits on the neutrino fluence were computed.
