Limits on sterile neutrino mixing using atmospheric neutrinos in Super-Kamiokande

TL;DR

This paper sets new limits on sterile neutrino mixing parameters using atmospheric neutrino data from Super-Kamiokande, finding no evidence for sterile oscillations and constraining the mixing angles for certain mass splittings.

Contribution

First limits on sterile neutrino mixing using atmospheric neutrinos in Super-Kamiokande with a large data set, assuming specific oscillation conditions and providing results in a generic format.

Findings

No evidence of sterile neutrino oscillations was observed.

Upper limits on mixing parameters: |U_{μ4}|^2 < 0.041, |U_{τ4}|^2 < 0.18 for Δm^2 > 0.8 eV^2.

Results are applicable to various sterile neutrino models.

Abstract

We present limits on sterile neutrino mixing using 4,438 live-days of atmospheric neutrino data from the Super-Kamiokande experiment. We search for fast oscillations driven by an eV$^2$-scale mass splitting and for oscillations into sterile neutrinos instead of tau neutrinos at the atmospheric mass splitting. When performing both these searches we assume that the sterile mass splitting is large, allowing $\sin^2(\Delta m^2 L/4E)$ to be approximated as $0.5$, and we assume that there is no mixing between electron neutrinos and sterile neutrinos ($|U_{e4}|^2 = 0$). No evidence of sterile oscillations is seen and we limit $|U_{\mu4}|^2$ to less than 0.041 and $|U_{\tau4}|^2$ to less than 0.18 for $\Delta m^2 > 0.8$ eV$^2$ at the 90% C.L. in a 3+1 framework. The approximations that can be made with atmospheric neutrinos allow these limits to be easily applied to 3+N models, and we provide our results in a generic format to allow comparisons with other sterile neutrino models.