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SEARCH FOR NEUTRINOS AT EXTREME ENERGIES WITH THE PIERRE AUGER OBSERVATORY
Marta Trini, doktorska disertacija

Opis: The detection of Ultra-High-Energy (UHE) neutrinos around and above 10 18 eV (1 EeV) can be the key to answering the long-standing question of the origin of the UHE cosmic rays. The Pierre Auger Observatory is the largest experiment that can detect the extensive air showers produced when the cosmic rays and neutrinos interact in the earth’s atmosphere. In particular, with the Infilled array of the Surface Detector of the Pierre Auger Observatory we can detect sub-EeV neutrino-induced particle showers. In this thesis we demonstrate that it is possible to discriminate neutrino-induced showers from the background showers produced by the more numerous nucleonic cosmic rays. The sensitivity to neutrinos is enhanced in the inclined directions with respect to the vertical to the ground, where cosmic ray-induced showers starting in the upper layers of the atmosphere are dominated by the muonic component of the shower, while deeply- penetrating neutrino showers in contrast exhibit a large electromagnetic component. Based on this idea in this thesis we have developed a search procedure for UHE neutrinos that consists on selecting inclined events in the Infilled array of the Pierre Auger Observatory in which the signals in the water-Cherenkov stations are spread in time, characteristic of the presence of electromagnetic component in the shower. We have established a complete chain of criteria to first select the inclined events among the sample of all events triggering the Infilled array, and then identifying those that have a large electromagnetic component at ground, and hence can be considered as neutrino candidates. We have identified a single variable, the so-called area-over-peak averaged over all of the stations in each event, as a suitable observable for neutrino identification purposes. The neutrino selection was established using extensive Monte Carlo simulations of the neutrino-induced showers in the Infilled array of Auger as well as a fraction of the data assumed to be totally constituted of background nucleonic cosmic rays. Using these neutrino simulations we have also computed the exposure of the Infilled array to UHE neutrinos in the period 1 January 04 - 31 December 2017. Associated systematic uncertainties on the exposure are also described. Expecting no candidate neutrinos in the period up to 31 December 2017, and adopting a differential neutrino diffuse flux dN ν /dE ν = k E ν −2 in the energy range from 0.05 to 1 EeV, we have obtained a 90% C.L. upper limit on the all neutrino flavor, k 90 < 7.97 × 10 −8 GeV cm −2 s −1 sr −1 .
Najdeno v: ključnih besedah
Ključne besede: astroparticles, astrophysical neutrinos, cosmic rays showers, Pierre Auger Observatory, Infilled array
Objavljeno: 03.10.2019; Ogledov: 642; Prenosov: 8
.pdf Polno besedilo (6,02 MB)

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