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Search for TeV-Scale Neutrino Dimuon Events with 10.7 Years of IceCube Data

  • Author / Creator
    Sarkar, Sourav
  • The IceCube neutrino observatory is a gigaton Cherenkov detector located at the geographic south pole. The experiment is designed to detect neutrinos originating from the atmosphere and astrophysical objects over a huge energy range from 10 GeV to 10 PeV. Information about the interacting neutrinos is extracted from the event reconstructions and identification of the event topologies, constituting probes to study high-energy particle physics and astrophysics. Typically, muon neutrinos produce a single muon from their interactions in ice via deep inelastic scattering (DIS) processes. However, in some fraction of the cases, the Standard Model predicts the production of two closely spaced high energy muons from the same neutrino interaction, referred to as dimuon. Detection of these events in IceCube can be a powerful tool to study rare standard model neutrino interactions and search for physics beyond the Standard Model at an energy scale beyond the reach of current accelerator neutrino experiments. However, identifying dimuon events in IceCube is very challenging due to the limited detector resolution, and no such events have been observed prior to this work.
    The primary contribution of the dimuon events within the Standard Model framework arises from the charm quark production in neutrino DIS processes. An additional subdominant standard model channel, called neutrino trident production, can also produce dimuon events. This thesis performs an inclusive search for such dimuon events in IceCube. The search analysis uses an event classification method developed based on advanced machine learning algorithms called graph neural networks to identify the dimuon events. The outcome of the event classification is then used to define two overlapping signal regions for the search. The analysis of 10.67 years of IceCube data used in this work reports the first non-zero observation of dimuon event candidates. A single event is observed in one signal region with a prediction of 0.21 background contamination, resulting in a dimuon signal significance of 1.31$\sigma$. The measurement in the second, higher statistics signal region reports the observation of 4 events against a background prediction of 2.13 events. The pure single muon background-only hypothesis is rejected at 1.15$\sigma$ for this region.

  • Subjects / Keywords
  • Graduation date
    Fall 2023
  • Type of Item
    Thesis
  • Degree
    Doctor of Philosophy
  • DOI
    https://doi.org/10.7939/r3-y8x0-mn08
  • License
    This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.