Explaining the MiniBooNE Excess Through a Mixed Model of Oscillation and Decay

Abstract

The electron-like excess observed by the MiniBooNE experiment is explained with a model comprising a new low mass state ($\mathcal{O}(1)$ eV) participating in neutrino oscillations and a new high mass state ($\mathcal{O}(100)$ MeV) that decays to $\nu+\gamma$. Short-baseline oscillation data sets are used to predict the oscillation parameters. Fitting the MiniBooNE energy and scattering angle data, there is a narrow joint allowed region for the decay contribution at 95% CL. The result is a substantial improvement over the single sterile neutrino oscillation model, with $\Delta \chi^2/dof$ = 19.3/2 for a decay coupling of $2.8 \times 10^{-7}$ GeV$^{-1}$, high mass state of 376 MeV, oscillation mixing angle of $7\times 10^{-4}$ and mass splitting of $1.3$ eV$^2$. This model predicts that no clear oscillation signature will be observed in the FNAL short baseline program due to the low signal-level.