Speaker
Description
The 4.8$\sigma$ low-energy excess (LEE) of electron-like events observed by MiniBooNE is one of the longest-standing anomalies in particle physics. As the MiniBooNE reconstruction relied on the identification of Cherenkov rings, the excess could come from extra electrons or photons in the detector. This talk covers new developments regarding each hypothesis. The MicroBooNE experiment has recently constrained the level to which excess $\nu_e$ interactions from the Booster Neutrino Beam can explain the LEE. We show that the MicroBooNE constraints are significantly alleviated if the LEE comes from $\overline{\nu}_e$ rather than $\nu_e$ interactions. This effect is due to a difference in the low-energy suppression of $\overline{\nu}_e$ and $\nu_e$ cross sections in carbon v.s. argon. Next, we discuss a model comprised of an eV-scale sterile neutrino and a heavy neutral lepton $\mathcal{N}$ with a transition magnetic moment coupling to active neutrinos, also known as a "neutrissimo". It is shown that the visible decay $\mathcal{N} \to \nu \gamma$ can explain the bulk of the energy and angular distributions of the LEE. New constraints on the neutrissimo model are also derived from MINER$\nu$A neutrino electron elastic scattering measurements. While they do not currently rule out the MiniBooNE solution, a dedicated MINER$\nu$A analysis would likely be sensitive to the MiniBooNE-preferred region of neutrissimo parameter space.
