Confirmation of the spectral excess in DAMIC at SNOLAB with skipper CCDs

We present results from a $3.25\text{ }\text{ }\mathrm{kg}\text{\ensuremath{-}}\mathrm{day}$ target exposure of two silicon charge-coupled devices (CCDs), each with 24 megapixels and skipper readout, deployed in the DAMIC setup at SNOLAB. With a reduction in pixel readout noise of a factor of 10 relative to the previous detector, we investigate the excess population of low-energy events in the CCD bulk previously observed above expected backgrounds. We address the dominant systematic uncertainty of the previous analysis through a depth fiducialization designed to reject surface backgrounds on the CCDs. The measured bulk ionization spectrum confirms the presence of an excess population of low-energy events in the CCD target with characteristic rate of $\ensuremath{\sim}7$ events per kg-day and electron-equivalent energies of $\ensuremath{\sim}80\text{ }\text{ }\mathrm{eV}$, whose origin remains unknown.