Exploration of Mass Splitting and Muon/tau Mixing Parameters for an Ev-Scale Sterile Neutrino with IceCube

We present the first three-parameter fit to a 3+1 sterile neutrino model using 7.634 years of data from the IceCube Neutrino Observatory on ν_μ+ν_μ charged-current interactions in the energy range 500–9976 GeV. Our analysis is sensitive to the mass-squared splitting between the heaviest and lightest mass state (Δ m_41^2), the mixing matrix element connecting muon flavor to the fourth mass state (|U_μ4|^2), and the element connecting tau flavor to the fourth mass state (|U_τ4|^2). Predicted propagation effects in matter enhance the signature through a resonance as atmospheric neutrinos from the Northern Hemisphere traverse the Earth to the IceCube detector at the South Pole. The remaining sterile neutrino matrix elements are left fixed, with |U_e4|^2= 0 and δ_14=0, as they have a negligible effect, and δ_24=π is set to give the most conservative limits. The result is consistent with the no-sterile neutrino hypothesis with a probability of 4.3 parameter yields the 90% confidence levels: 2.4 eV^2 < Δ m_41^2 <9.6 eV^2 , 0.0081 < |U_μ4|^2 < 0.10 , and |U_τ4|^2< 0.035, which narrows the allowed parameter-space for |U_τ4|^2. However, the primary result of this analysis is the first map of the 3+1 parameter space exploring the interdependence of Δ m_41^2, |U_μ4|^2, and |U_τ4|^2.