Measurement of the ionization produced by sub-keV silicon nuclear recoils in a CCD dark matter detector

Understand

We report a measurement of the ionization efficiency of silicon nuclei recoiling with sub-keV kinetic energy in the bulk silicon of a charge-coupled device (CCD).

• Nuclear recoils are produced by low-energy neutrons ($<$24 keV) from a $^{124}$Sb-$^{9}$Be photoneutron source, and their ionization signal is measured down to 60 eV electron equivalent.
• This energy range, previously unexplored, is relevant for the detection of low-mass dark matter particles.
• The measured efficiency is found to deviate from the extrapolation to low energies of the Lindhard model.