Search for astrophysical tau neutrinos using 7.5 years of IceCube data

• Main Author: Meier, Maximilian
• Other Authors: Rhode, Wolfgang, Spaan, Bernhard
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: 2019
• Subjects: ddc:530; Astroteilchenphysik; Tau Neutrinos; IceCube; Astroparticle physics; South Pole; South pole
• Online Access: http://hdl.handle.net/2003/38403; https://doi.org/10.17877/DE290R-20335

Astrophysical tau neutrinos are the last unidentified standard model messenger in astroparticle physics. Their identification can open new windows to neutrino physics, improve knowledge about cosmic neutrino sources and even test physics beyond the standard model. This work aims to constrain the tau neutrino component in the astrophysical neutrino flux observed by the IceCube Neutrino Observatory. Due to neutrino oscillations over cosmic baselines, a significant fraction of tau neutrinos is expected regardless of the exact neutrino production scenario at cosmic sources. The IceCube detector instruments a volume of 1 km3 to detect neutrinos interacting with the glacial ice at the South Pole at a depth between 1450 m and 2450 m. This is achieved by 5160 digital optical modules (DOMs), each equipped with a photomultiplier tube detecting Cherenkov light produced by secondary particles from neutrino interactions. In this dissertation, a new tau neutrino identification method is developed using state-of-the-art machine learning techniques to increase the expected tau neutrino event rate by a factor of 2.5 over previous work. Tau neutrinos are identified by the so-called double pulse signature, where two charge depositions can be observed in the waveform recorded in a single IceCube DOM: the first from the hadronic cascade induced by the neutrino interaction; the second one from a non-muonic decay of the produced tau lepton. This signature can be resolved by IceCube at energies above roughly 100 TeV. IceCube data recorded from 2011 to 2018 is analyzed and two tau neutrino candidates are observed. The astrophysical tau neutrino flux normalization is measured with a binned Poisson likelihood fit and the flux is observed to be 0.44+0.78 −0.31 10−18 GeV−1 cm−2 s−1 sr−1 at 100 TeV for an astrophysical spectral index of ???? = 2.19. The observation is found to be incompatible with the non-observation of a tau neutrino flux at a significance of 1.9????. Astrophysikalische Tau-Neutrinos sind das letzte nicht identifizierte ...