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Development of multi-messenger real-time analyses for the KM3NeT neutrino telescope

Abstract : Since the discovery of the cosmic-ray radiation at the beginning of the 20th century, the hunt for their sources has been driving the research into the most energetic phenomena in the Universe. Astronomy has developed consequently, first with the exploration of the non-visible portion of the electromagnetic spectrum known as multi-wavelength astronomy. The perspective has been widened further by multi-messenger astronomy, with the notable discoveries of gravitational waves and of the astrophysical neutrino flux. Neutrinos in particular emerge as a formidable cosmic messenger. Being light, neutral and weakly-interacting particles, they can travel unperturbed over cosmic distances, overcoming the limits of electromagnetic radiation (absorption) and charged particles (deflection by magnetic fields). Their emission is also especially revealing of the astrophysical properties of the source. For cosmic-ray source candidates, high-energy neutrinos would be an unequivocal signature of occurring hadronic acceleration processes. Whereas IceCube and ANTARES have observed the astrophysical neutrino flux, its origin is not yet established. In the special case of core-collapse supernovae, low-energy neutrinos carry more than 99% of the star gravitational energy and are believed to drive the explosion mechanism. These are observable only for galactic or near-galactic events, and only one event, SN 1987A, has been recorded since the beginning of the neutrino era. This scenario calls for the design and construction of a new generation of neutrino telescopes. By instrumenting two deep-sea sites with digital optical modules, for a total of ~ 200 000 photomultiplier tubes, the KM3NeT ORCA and ARCA detectors will address the open questions on the neutrino mass ordering and the sources of astrophysical neutrinos, respectively. The analyses presented in this thesis exploit the KM3NeT design by analysing the coincidences detected by the 31 PMTs of each optical module. The first part of this work consists of a measurement of the atmospheric muon rate as a function of the sea depth in the depth range between 2200 and 3500 m, performed with the first three detection units across the two sites. The result is compatible with a state-of-the-art model of the underwater muon flux within the systematic uncertainties. The analysis has been instrumental to the validation of the detector time and efficiency calibration, and to the development of the simulation procedures. The main subject of this thesis is the determination of the KM3NeT capability of detecting a galactic core-collapse supernova event resulting in a neutrino burst on the 10 MeV energy scale. The development of the background filtering and event selection strategy is described in detail. The discovery sensitivity is evaluated by comparison with a simulation of the signal expected from the neutrino flux, as predicted by advanced three-dimensional models of a supernova explosion. The implementation of the analysis algorithm in an online trigger application is described, together with the first implementation of the real-time multi-messenger infrastructure for KM3NeT. The alert generation mechanism and its integration in the global SNEWS alert network are introduced. The first follow-up analyses of gravitational wave alerts are reported. The last part of this work addresses the absolute pointing of the detector, which accuracy is important to the full exploitation of the sub-tenth of degree resolution of KM3NeT at high-energy. With the ORCA detector as a test-bed, a procedure exploiting acoustic multilateration and beamforming techniques is proposed to determine the absolute position of the detection units on the seafloor and subsequently verify the pointing accuracy of the telescope.
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https://hal.archives-ouvertes.fr/tel-03109402
Contributor : Massimiliano Lincetto <>
Submitted on : Thursday, March 4, 2021 - 2:25:02 PM
Last modification on : Monday, March 29, 2021 - 3:22:57 PM

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Massimiliano Lincetto. Development of multi-messenger real-time analyses for the KM3NeT neutrino telescope. High Energy Physics - Experiment [hep-ex]. Aix-Marseille Université, 2020. English. ⟨tel-03109402v2⟩

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