Resumen de Characterization of the optical properties at the ANTARES site using the Optical Beacon system. Influence on the detector performance
Harold Yepes Ramirez
Neutrino Astronomy aims to scientifically exploit neutrinos as a new cosmic messenger to explore high energy astrophysical phenomena in the TeV-PeV energy range. The very low fluxes and the small interaction crosssection of neutrinos with matter require the construction of massive detectors. When the incoming neutrino direction can be reconstructed with a reasonable angular accuracy, the detector is dubbed "telescope", since the neutrinos, having no electric charge, point back to their source. In the Cherenkov technique, the observation of the neutrino is carried out through the detection of the Cherenkov light induced by the charged relativistic particles produced in the neutrino interaction with matter, mainly the muon in the case of the charged current interactions of muon neutrinos. From the arrival time and position of the detected Cherenkov photons induced by those secondary particles which cross the medium where the detector is located, information on the neutrino direction and energy can be inferred. Since the optical properties of the medium in which the telescope is located determine the transmission of the Cherenkov photons, a proper understanding of the influence of these properties in the track reconstruction and detector performance is required. The ANTARES deep-sea neutrino detector is the first fully operational undersea neutrino telescope in the Northern Hemisphere. It consists in a three-dimensional layout of 885 photomultipliers (PMTs) arranged in 12 detection lines plus one instrumentation line. Each detection line has 25 storeys, each of them containing triplets of PMTs housed in optical modules (OMs) and independent modules with the associated electronics. Some of these storeys are equipped with extra devices for time calibration and positioning of the detector. The Optical Beacon system, in particular, was designed for the in-situ time calibration of the apparatus, i.e. for the proper synchronization of its OMs. Although originally designed to this end, the OB system can be used to have a handle on the optical properties of the surrounding water. The objective of this thesis is to characterize the ANTARES detection medium. In this sense, some optical properties of the water namely, transmission, absorption and effective scattering lengths are measured with the OB system. Additionally, a complementary study on how such properties influence the reconstruction of tracks and the detector performance is carried out. To reach this goal, special calibration runs were commissioned and new instruments for water properties measurements were built and operated, e.g. the multiwavelength beacon and the nano-beacons. The tuning of the operating parameters and the handling of such devices once installed in the detector were also tasks performed during this work to achieve the aforementioned goal. Likewise, the development of specialised software codes for calibration and physical analyses together with the production of large simulation samples were, in addition, an important part of this work.
