Precision Measurements of Nuclear Recoil Ionization in Silicon Skipper CCDs for Dark Matter Detection*

Dark matter detection via nuclear scatters is heavily dependent on the ionization efficiency of the target. As silicon detectors approach an increased sensitivity down to Ο(10eV), we need precise calibration measurements of the ionization efficiency. We use a silicon skipper charge-coupled device (CCD) with single-electron resolution developed for the DAMIC-M experiment to perform the measurement. A ¹²⁴Sb-⁹Be source was used to generate neutrons (~23 keV), and Monte Carlo simulations were used to model the nuclear recoil spectrum. In this talk, we will report the measured ionization efficiency and compare it with the low energy extrapolations of the Lindhard model and previous measurements.