Neutrino physics beyond the minimal Standard Model with IceCube DeepCore and PINGU
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Abstract
The observation of neutrino flavour transitions including the periodic “oscillation” phenomenon has led to increasingly deep insights into the nature of leptonic mass-flavour mixing and the neutrino mass spectrum. Ever since the earliest experiments, new neutrino interactions have also been scrutinised as an additional mechanism that could give rise to flavour transitions in the terrestrial or solar medium. This thesis presents two studies with very-large-volume Cherenkov detectors in deep glacial ice at the Geographic South Pole which investigate the flavour-, energy-, and zenith-dependent signatures of the aforementioned physics beyond the minimal Standard Model on the flux spectra of neutrinos produced in the Earth’s atmosphere.
The first study makes use of a sample of atmospheric neutrino events created from three years of operation with the existing IceCube DeepCore detector, with energies from 5.6 GeV to 100 GeV, in order to search for and constrain neutral-current non-standard interactions which modify the potential for coherent forward scattering encountered by atmospheric neutrinos as they propagate through the Earth. The measurement consists of separate tests of several hypotheses about the flavour structure of the interactions in the presence of standard oscillations and reports limits on effective coupling strengths for Earth matter. While oscillation measurements in general are not sensitive to the scale of flavour-diagonal interactions, which corresponds to an unobservable phase common to all of the propagating neutrino states, the vanishing four-momentum transfer in forward scattering renders them independent of the energy scale of the physics beyond the Standard Model.
The second analysis solely draws from the Monte Carlo simulation of the detector response of the proposed IceCube low-energy upgrade PINGU, whose dense instrumentation is expected to lead to a lowered energy threshold of ∼1 GeV and improved reconstruction capabilities for GeV-scale atmospheric neutrinos. Working within a frequentist statistical framework, different approaches to projecting PINGU’s sensitivity to the still unresolved ordering of the neutrino mass eigenstates are discussed, assuming standard neutrino interactions with Earth matter. In particular, the sensitivity dependence on the values of the atmospheric neutrino oscillation parameters, the leptonic mixing angle θ₂₃ and the mass-squared difference Δm²₃₁, is investigated in detail.