What sets the residual single-electron event rate in skipper CCDs?
In plain words
Skipper CCDs can count single electrons, but they register stray single electrons at a low steady rate that mimics the faintest dark matter signals. The question is where these stray electrons come from and how low the rate can go.
Precise statement
Skipper CCDs (SENSEI, DAMIC-M, Oscura) measure a rate of 1-electron events per pixel per day that limits searches for dark matter-electron scattering in the 1-2 electron bins. Candidate sources are thermal dark current, spurious charge from readout clocking, Cherenkov and recombination photons from high-energy tracks, and charge release from defects. An answer is a quantitative decomposition of the measured rate into sources and the irreducible floor for silicon at the operating temperature.
What would settle it
Rate measurements versus temperature, clocking scheme, readout timing, shielding and track density in otherwise identical CCDs, compared with a calibrated source model.
Status in the literature
Unverified note
The 2025 DAMIC-M prototype search (Phys. Rev. Lett. 135, 071002) ran with a 50-fold lower single-electron rate than its previous search, showing much of the earlier rate was instrumental; the floor is not known.