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Title: What causes the bulk ionization excess in DAMIC CCDs at SNOLAB?
Plain: Silicon camera chips used to search for dark matter deep underground see extra small charge signals from inside the silicon, beyond all known radioactivity. The cause is unknown.
Precise: DAMIC at SNOLAB reported an excess of bulk ionization events above the radiogenic background model, with characteristic rate about 7 events/(kg day) at electron-equivalent energies about 80 eV, later confirmed with skipper CCDs. An answer identifies the source (unmodeled background such as low-energy Compton or surface events, a detector effect, or new physics) and predicts the rate and spectrum in other silicon detectors.
Settled by: Comparison of the bulk excess across silicon CCDs with different fabrication, depth, shielding and cosmogenic exposure (DAMIC-M, SENSEI, Oscura prototypes) and with calibrated low-energy Compton spectra.
Kind: phenomenon
Answer type: identification
References: (empty)
Literature status: open
Status note: Confirmed with skipper CCDs at SNOLAB (Phys. Rev. D 109, 062007, 2024, arXiv 2306.01717); origin unknown.
Posed since: 2020