Explaining the MiniBooNE excess through a mixed model of neutrino oscillation and decay

The electronlike excess observed by the MiniBooNE experiment is explained with a model comprising a new low mass state ($\mathcal{O}(1)\mathrm{eV}$) participating in neutrino oscillations and a new high mass state ($\mathcal{O}(100)\mathrm{MeV}$) that decays to $\nu +\gamma$. Short-baseline oscillation datasets 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 $\mathrm{\Delta }{\chi }^2/\mathrm{dof}=19.3/2$ for a decay coupling of $2.8\times {10}^{-7}{\mathrm{GeV}}^{-1}$, high mass state of 376 MeV, oscillation mixing angle of $7\times {10}^{-4}$ and mass splitting of $1.3{\mathrm{eV}}^2$. This model predicts that no clear oscillation signature will be observed in the FNAL short baseline program due to the low signal-level.

Figure 1

$\mathcal{N}$ production from ${\pi }^0$ Dalitz decay (left) and $\nu$ upscattering (middle), and decay (right).

Figure 2

Preferred regions to explain the MiniBooNE excess in $E_{\nu }^{QE}$ (pink) and $\cos \theta$ (green) as a function of dipole coupling and $\mathcal{N}$ mass. The black star indicates $\{d,m_{\mathcal{N}}\}=\{2.8\times {10}^{-7}{\mathrm{GeV}}^{-1},376\mathrm{MeV}\}$, which lies in the joint 95% CL allowed region for both distributions. Constraints from other experiments are also shown at the 95% CL.

Figure 3

$E_{\nu }^{QE}$ (left) and $\cos \theta$ (right) distributions of the MiniBooNE excess for a representative point of the $3+1+\mathcal{N}$-decay model. The error bars on the energy distribution include systematic and statistical errors, while for the angular distribution only statistical errors are included.