Results on Low-Mass Weakly Interacting Massive Particles from an 11 kg-day Target Exposure of DAMIC at SNOLAB

Understand

We present constraints on the existence of weakly interacting massive particles (WIMPs) from an 11 kg-day target exposure of the DAMIC experiment at the SNOLAB underground laboratory.

• The observed energy spectrum and spatial distribution of ionization events with electron-equivalent energies $>$200 eV$_{\rm ee}$ in the DAMIC CCDs are consistent with backgrounds from natural radioactivity.
• An excess of ionization events is observed above the analysis threshold of 50 eV$_{\rm ee}$.
• While the origin of this low-energy excess requires further investigation, our data exclude spin-independent WIMP-nucleon scattering cross sections $\sigma_{\chi-n}$ as low as $3\times 10^{-41}$ cm$^2$ for WIMPs with masses $m_{\chi}$ from 7 to 10 GeV$c^{-2}$ .