Sub-GeV dark matter and low energy neutrino-nucleus scattering experiments require extremely low energy thresholds and minimal background levels. While an extensive research is being carried out to push the sensitivity of particle detectors, an unknown type of background affects basically all low-threshold experiments in the field. This background has an energy spectrum that sharply rises at low energy, precisely in the signal region, and a complete understanding of its origin(s) is still an open question.
In this talk I will investigate this “low energy excess”, focusing on its features and possible explanations.