Speaker
Description
We present results from a 3.1 kg-day target exposure of two 24-megapixel skipper charge-coupled devices (CCDs) deployed in the DAMIC setup at SNOLAB. With a $10\times$ reduction in pixel noise, we investigate the excess population of low-energy bulk events previously observed. We address the dominant systematic uncertainty of the previous analysis through an improved strategy to reject CCD surface backgrounds by depth fiducialization. The observed energy spectrum and spatial distribution of ionization events with electron-equivalent energies $<$500 eV confirm the presence of a bulk excess compatible with previous findings. This measurement establishes the existence of a prominent source of low-energy events in the CCD target with characteristic rate of ${\sim}10$ events per kg-day, and energies ${\sim}100~$eV, whose origin remains unknown.
| Submitted on behalf of a Collaboration? | Yes |
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