On the annual modulation signal in dark matter direct detection

TL;DR

This paper establishes model-independent bounds on annual modulation signals in dark matter detection experiments, linking them to unmodulated event rates and applying these bounds to experimental data from DAMA and CoGeNT.

Contribution

It derives general and more stringent bounds on annual modulation signals based on unmodulated rates, applicable across various dark matter models and backgrounds.

Findings

DAMA's modulation signal satisfies the derived bounds.

Severe restrictions on dark matter mass are found for CoGeNT.

Bounds are valid under broad assumptions, including unknown backgrounds.

Abstract

We derive constraints on the annual modulation signal in Dark Matter (DM) direct detection experiments in terms of the unmodulated event rate. A general bound independent of the details of DM distribution follows from the assumption that the motion of the earth around the sun is the only source of time variation. The bound is valid for a very general class of particle physics models and also holds in the presence of an unknown unmodulated background. More stringent bounds are obtained, if modest assumptions on symmetry properties of the DM halo are adopted. We illustrate the bounds by applying them to the annual modulation signals reported by the DAMA and CoGeNT experiments in the framework of spin-independent elastic scattering. While the DAMA signal satisfies our bounds, severe restrictions on the DM mass can be set for CoGeNT.