The DAMIC excess from WIMP-nucleus elastic scattering

TL;DR

This paper reports an excess of low-energy events in DAMIC CCDs potentially caused by WIMP-nucleus elastic scattering, highlighting scenarios where this interpretation remains consistent with other experimental constraints.

Contribution

It identifies specific isospin-violating and spin-dependent scenarios that could explain the DAMIC excess as WIMP interactions, despite previous exclusions.

Findings

Observed low-energy events are consistent with WIMPs of 2-4 GeV mass.

Standard spin-independent WIMP models are excluded by argon-based experiments.

Certain isospin-violating and spin-dependent models remain viable explanations.

Abstract

Two dark matter searches performed with charge-coupled devices (CCDs) in the DAMIC cryostat at SNOLAB reported with high statistical significance the presence of an unidentified source of low-energy events in bulk silicon. The observed spectrum is consistent with nuclear recoils from the elastic scattering of weakly interacting massive particles (WIMPs) with masses between 2 and 4 GeV. In the standard scenario of spin-independent WIMP-nucleus scattering, the derived cross section is conclusively excluded by results in argon by the DarkSide-50 experiment. We identify isospin-violating and spin-dependent scenarios where interactions with $^{40}$Ar are strongly suppressed and the interpretation of the DAMIC excess as WIMP-nucleus elastic scattering remains viable.