Electrovolt-scale backgrounds from surfaces

Recent results from the SENSEI experiment show that a cut on event clustering can reduce low-energy excesses in their eV-sensitive calorimeter. This hints at the role of surrounding uninstrumented surfaces in producing backgrounds. Charged particles crossing dielectric boundaries are well known to produce low-energy radiation. In particular, transition radiation, secondary electron emission, and sputtering may contribute to the spectrum, morphology, and rate of events observed in eV-sensitive detectors. The rich phenomenology and high yields of these surface processes will complicate comparisons of low-threshold dark matter detectors both to each other and to background models.