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

TL;DR

This paper reports constraints on low-mass WIMPs from DAMIC's 11 kg-day exposure, setting new limits on WIMP-nucleon cross sections for masses 7-10 GeV, and discusses an unexplained low-energy event excess.

Contribution

It provides the strongest silicon-based constraints on low-mass WIMPs and relates findings to previous CDMS silicon results, with new experimental data from DAMIC.

Findings

Excludes WIMP-nucleon cross sections down to 3×10⁻⁴¹ cm² for 7-10 GeV WIMPs.

Detects an unexplained excess of low-energy ionization events.

Sets new limits on low-mass WIMPs, impacting dark matter models.

Abstract

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$c^{-2}$ . These results are the strongest constraints from a silicon target on the existence of WIMPs with $m_{\chi}$$<$9 GeV$c^{-2}$ and are directly relevant to any dark matter interpretation of the excess of nuclear-recoil events observed by the CDMS silicon experiment in 2013.