HEP In the literature: open

What is the source of the MiniBooNE low-energy excess?

In plain words

MiniBooNE saw extra events at low energy that look like electrons, but its detector could not tell electrons from photons.

Precise statement

Identify whether the MiniBooNE low-energy excess (reconstructed $E_{\nu}$ between 200 and 475 MeV) is from electrons, single photons, e+e- pairs or mismodeled backgrounds such as $\Delta \to \mathrm{N}\gamma$ and $\pi0$ misidentification. An answer assigns the excess to a specific final state with $\ge 3\sigma$ confidence.

What would settle it

Liquid-argon TPC measurements in the same beam that separate electrons from photons by dE/dx (MicroBooNE, SBND, ICARUS).

Status in the literature

Unverified note

MicroBooNE results (2021 to 2025) disfavor $\nu_e$ and $\Delta$ radiative explanations of the full excess, leaving its source unidentified.