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Thesis Defense
A Few New Techniques for Probing IceCube Data and a Search for High Energy Atmospheric Neutrinos
Date: Thursday, August 25th
Time: 2:00 pm
Speaker: Bunheng Ty, Physics PhD Graduate Student
Abstract: The idea of characterizing an IceCube event by its location and magnitude of maximum photon density is proven useful. A complete set of new filter tools built around this idea is successfully developed and used to detect high-energy neutrino interactions inside IceCube. The two key features to search for are: a highly localized deposit of photoelectrons, and a lack of a veto track leading up to it. The first is achieved reliably by counting photoelectrons making up the most photon-dense region of the event. The second is achieved with moving cylinders (160 m radius, 240 m half-height, 0.3 m/ns speed), one at each possible direction from the sky, collecting any DOM forming a muon track pattern with the region. In addition to the traditional true starting events, this new approach allows, for the first time, a direct search for the self-veto events of the atmospheric neutrinos. The no-veto condition is loosened to allow up to a very small veto, just enough to be still outside the region of the atmopsheric muon background. The final selection consists of 23 events, one of which is a self-veto event of 134 TeV Millipede reconstructed energy. This data, though limited, shows a measurable contribution of the atmospheric component to the neutrino flux at the high energies. A lower bound estimate is given for the atmospheric contribution to IceCube’s HESE sample to be at least at the level of 1 percent.
Host: Kael Hanson
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