Measurement of Compton scattering on silicon atomic shell electrons with Skipper CCDs

For direct detection searches, reaching detector energy thresholds $\mathcal{O}(10\,eV)$ is necessary for sensitivity to low-mass dark matter candidates. In this regime, ionization signals from small-angle Compton scattering of environmental $\gamma$-rays need to be calibrated for proper background estimatation in silicon-based detectors, such as DAMIC-M. Using $^{241}$Am and $^{57}$Co $\gamma$-ray sources, we report the first measurements of scattering on silicon atomic shell electrons in a Skipper charged-coupled device (CCD) with single-electron resolution. Agreement between data and a theoretically-motivated parameterization of the spectral features will be discussed.