The MiniBooNE anomaly and heavy neutrino decay

Abstract

The anomaly in the low energy distribution of quasi-elastic neutrino events reported by the MiniBooNE collaboration is discussed. We show that the observed excess of electron-like events could originate from the production and decay of a heavy neutrino ($ν_h$) in the MiniBooNE detector. The $ν_h$ is created by mixing in $ν_μ$ neutral-current interactions and decays radiatively into $ νγ$ due to a transition magnetic moment between the $ν_h$ and a light neutrino $ν$. The energy measured in the detector arises from the subsequent conversion of the decay photon into a $\pair$ pair within the detector volume. The analysis of the energy and angular distributions of the excess events suggests that the $ν_h$ has a mass around 500 MeV and the lifetime $τ_{ν_h} \lesssim 10^{-9}$ s. Existing experimental data are found to be consistent with a mixing strength between the $ν_h$ and the $ν_μ$ of $|U_{μh}|^2 \simeq (1-4)\times 10^{-3}$ and a $ν_h$ transition magnetic moment of $ μ_{tr} \simeq (1- 6)\times 10^{-9} μ_B$. Finally, we discuss the reason why no significant excess of low energy events has been observed in the recent antineutrino data.