First Search for Unstable Sterile Neutrinos with the IceCube Neutrino Observatory

TL;DR

This study searches for unstable sterile neutrinos using eight years of IceCube atmospheric muon neutrino data, finding no evidence for decay but constraining sterile neutrino parameters and excluding certain regions from previous experiments.

Contribution

First search for unstable sterile neutrinos with IceCube data, providing new constraints on decay parameters and challenging existing short-baseline oscillation results.

Findings

No significant evidence for sterile neutrino decay.

Best-fit decay parameters: Δm₄₁² ≈ 6.7 eV², sin²2θ₂₄ ≈ 0.33.

Excluded regions from short-baseline experiments at 90% C.L.

Abstract

We present a search for an unstable sterile neutrino by looking for a matter-induced signal in eight years of atmospheric $\nu_\mu$ data collected from 2011 to 2019 at the IceCube Neutrino Observatory. Both the (stable) three-neutrino and the 3+1 sterile neutrino models are disfavored relative to the unstable sterile neutrino model, though with $p$-values of 2.5\% and 0.81\%, respectively, we do not observe evidence for 3+1 neutrinos with neutrino decay. The best-fit parameters for the sterile neutrino with decay model from this study are $\Delta m_{41}^2=6.7^{+3.9}_{-2.5}\,\rm{eV}^2$, $\sin^2 2\theta_{24}=0.33^{+0.20}_{-0.17}$, and $g^2=2.5\pi\pm1.5\pi$, where $g$ is the decay-mediating coupling. The preferred regions from short-baseline oscillation searches are excluded at 90\% C.L.