Characterizing cosmic neutrino sources

• Main Author: Mohrmann, Lars
• Format: Thesis
• Language: English
• Published: Deutsches Elektronen-Synchrotron, DESY, Hamburg 2015
• Subjects: South Pole; South pole
• Online Access: https://dx.doi.org/10.3204/pubdb-2017-11587; http://bib-pubdb1.desy.de/record/393644

Humboldt Universität, Dissertation, 2015; Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät, 233 p. (2015). doi:10.18452/17377 = Humboldt Universität, Dissertation, 2015 : The IceCube Neutrino Observatory is a km$^3$-sized neutrino telescope located at the geographical South Pole. Its primary purpose is the detection of high-energy cosmic neutrinos. Such neutrinos are expected to be produced in interactions of high-energy cosmic rays with ambient matter or photons close to their acceleration sites. The IceCube Collaboration has reported the first evidence for a flux of high-energy cosmic neutrinos. While the origin of the flux remains unknown so far, the properties of its sources can be constrained by measuring its energy spectrum and its composition of electron, muon, and tau neutrinos. The present work constitutes the first comprehensive analysis of IceCube data with respect to these principal characteristics of the flux. Several data sets were assembled and simultaneously studied in a combined analysis. Experimentally observed distributions of reconstructed energy, zenith angle and particle signature were fitted with model distributions. Assuming the cosmic neutrino flux to be isotropic and to consist of equal flavors at Earth, the all-flavor spectrum is well described by a power law with normalization $(6.7_{-1.2}^{+1.1})x10^{-18}GeV^{-1}s^{-1}sr^{-1}cm^{-2}$ at 100 TeV and spectral index -2.50$\pm$0.09 for neutrino energies between 25 TeV and 2.8 PeV. A spectral index of -2 is disfavored with a significance of 3.8 standard deviations. The flavor composition is compatible with that expected for standard neutrino production processes at the sources. However, a scenario in which only electron neutrinos are produced is disfavored with a significance of 3.6 standard deviations. Assuming that standard neutrino oscillations transform the neutrino flavors during propagation from the sources to the Earth, the measured fraction of electron neutrinos at Earth is (18$\pm$11)%. These results constitute the most precise characterization of the cosmic neutrino flux observed with the IceCube Neutrino Observatory obtained so far. : Published by Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät