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 (Δm₄₁²), 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 δ₁₄=0, as they have a negligible effect, and δ₂₄=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%. Profiling the likelihood of each parameter yields the 90% confidence levels: 2.4eV²<Δm₄₁²<9.6eV², 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 Δm₄₁², |U_μ4|², and |U_τ4|².