Thesis Defense

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Thesis Defense
Measurement of the Astrophysical Diffuse Neutrino Flux using Starting Track Events in IceCube
Date: Wednesday, June 14th
Time: 11:00 am - 1:00 pm
Place: 4274 Chamberlin and
Speaker: Manuel Silva, Department of Physics Graduate Student
Abstract: Since the discovery of cosmic rays by Victor Hess in 1912, there have been numerous advances in the field including but not limited to: larger cosmic ray detectors, observatories searching for gamma-rays and astrophysical neutrinos. This dissertation focuses on neutrinos since they are neutral and light making them the optimal messenger. By measuring the neutrino flux, we can better under the mechanisms by which these cosmic rays are created. In 2013, the IceCube collaboration first announced the observation of these astrophysical neutrinos launching us into the era of high energy neutrino astrophysics. This work summarizes a novel dataset, searching for starting track events, whereas a neutrino interacts within the fiducial volume of the detector producing a muon track. This event morphology is of particular importance as it enables us to measure the energy of the event to within 25% error and the direction of the event to within 1.5◦ error. Utilizing 10.3 years of IceCube data, we characterize the astrophysical diffuse neutrino flux. Using a single power law flux, we measure the spectral index as γ = 2.58+0.10−0.09 and the per-flavor normalization as ΦAstro per−flavor = 1.68+0.19 −0.22 (at 100 TeV). The sensitive energy range to this flux is 3-550 TeV making this the lowest energy astrophysical flux measurement to date. We also show structure (or lack thereof) in the flux towards lower energies by using a broken power law. We reject γ &lt; 1 to 3σ significance and γ &lt; 2 to 2.1σ significance below a break energy of 25 TeV.
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