Decaying sterile neutrinos at short baselines

TL;DR

This paper investigates whether decaying sterile neutrinos can explain short-baseline neutrino anomalies, using new MicroBooNE data to constrain models and assess their viability in resolving longstanding experimental tensions.

Contribution

It provides new limits on decaying sterile neutrino models based on MicroBooNE data and offers an updated fit to MiniBooNE results, evaluating the decaying neutrino hypothesis.

Findings

MicroBooNE data strongly constrains decaying sterile neutrino models

The decaying sterile neutrino solution is largely ruled out at over 99% confidence level

Updated MiniBooNE fit shows persistent tension with sterile neutrino decay scenarios

Abstract

Long-standing anomalous experimental results from short-baseline neutrino experiments have persisted for decades. These results, when interpreted with one or more light sterile neutrinos, are inconsistent with numerous null results experimentally. However, if the sterile neutrino decays en route to the detector, this can mimic $\nu_\mu \to \nu_e$ oscillation signals while avoiding many of these external constraints. We revisit this solution to the MiniBooNE and LSND puzzles in view of new data from the MicroBooNE experiment at Fermilab. Using MicroBooNE's liquid-argon time-projection chamber search for an excess of $\nu_e$ in the Booster beam, we derive new limits in two models' parameter spaces of interest: where the sterile neutrino decays (I) via mixing with the active neutrinos, or (II) via higher-dimensional operators. We also provide an updated, comprehensive fit to the MiniBooNE neutrino- and antineutrino-beam data, including appearance ($\nu_e$) and disappearance ($\nu_\mu$) channels. Despite alleviating the tension with muon neutrino disappearance experiments, we find that the latest MicroBooNE analysis rules out the decaying sterile neutrino solution in a large portion of the parameter space at more than $99\%$ CL.