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Dissertation
A multi-channel, simultaneous fit approach to neutrino source searches: combining tracks and cascades in IceCube
Doctor of Philosophy (Ph.D.), Drexel University
Dec 2025
DOI:
https://doi.org/10.17918/00011253
Abstract
The origin of high-energy cosmic rays remains one of astrophysics' most enduring mysteries. Neutrinos produced in cosmic-ray interactions provide a direct probe of their sources, as they travel undeflected by magnetic fields. This work presents searches for astrophysical neutrino sources using the IceCube Neutrino Observatory, introducing and implementing, for the first time, a simultaneous fit of different event topologies in both time-integrated and time-dependent analyses. The topologies used in this work were track-like events and cascade-like events. The combined dataset incorporates 14-15 years of track data and 10-12 years of cascade data, which, by leveraging tracks superior pointing ability and cascades superior energy resolution, yields the most sensitive all-sky point-source search to date. An all-sky scan identifies NGC 1068 as the most significant northern-sky source, with a post-trial significance of 3.5[sigma]. A time-dependent flare search excludes Gaussian flares shorter than 708 days as the origin of NGC 1068's emission, representing the first such constraint on this confirmed neutrino source. A Galactic plane template analysis tests three diffuse emission models. While tracks alone yield no significant detection (1.74[sigma]), adding two years of data to the previous cascade dataset, most recently used to find evidence of neutrino emission from the Milky Way at the 4.5[sigma] level, achieves a significance of 5.66[sigma]. The combined track-and-cascade template analysis reaches an even higher 5.75[sigma] post-trial, further strengthening the evidence for neutrino emission from the Galactic plane. These results demonstrate that combining datasets with different neutrino event morphologies improves both sensitivity and discovery potential in a wide range of searches for high-energy neutrino sources.
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Details
- Title
- A multi-channel, simultaneous fit approach to neutrino source searches
- Creators
- Riya Atul Shah
- Contributors
- Naoko Kurahashi Neilson (Advisor) - Drexel University, Physics
- Awarding Institution
- Drexel University
- Degree Awarded
- Doctor of Philosophy (Ph.D.)
- Publisher
- Drexel University
- Number of pages
- xiv, 73 pages
- Resource Type
- Dissertation
- Language
- English
- Academic Unit
- College of Arts and Sciences; Physics; Drexel University
- Other Identifier
- 991022150938404721