Inelastic Dark Matter and DAMA/LIBRA: An Experimentum Crucis

TL;DR

This paper discusses the DAMA/LIBRA annual modulation signal and explores inelastic dark matter as a compatible explanation, proposing a directional detection experiment to definitively test this hypothesis and constrain the scenario.

Contribution

It introduces a directional detection experiment as a crucial test for the inelastic dark matter explanation of DAMA/LIBRA's signal.

Findings

Directional detection can sharply distinguish inelastic dark matter signals.

Proposed experiment with ~1000 kg day exposure constrains DAMA/iDM scenario.

Estimated significance depends on WIMP parameters and background rates.

Abstract

The DAMA/LIBRA collaboration has detected an annual modulation of the recoil rate in NaI crystals with the phase expected for WIMP scattering events. This signal is dramatically inconsistent with upper limits from other experiments for elastically scattering weak-scale WIMPs. However, the results are compatible for the case of inelastic dark matter (iDM). The iDM theory, as implemented by Tucker-Smith and Weiner, constrains the WIMP to a tight contour in sigma_n-delta space, where delta is the mass difference between the ground state and excited WIMPs. An urgent priority in direct detection is to test this scenario. The crucial test of the iDM explanation of DAMA -- an "experimentum crucis" -- is an experiment with directional sensitivity, which can measure the daily modulation in direction. Because the contrast can be 100%, it is a sharper test than the much smaller annual modulation in the rate. We estimate the significance of such an experiment as a function of the WIMP mass, cross section, background rate, and other parameters. The proposed experiment severely constrains the DAMA/iDM scenario even with modest exposure (~1000 kg day) on gaseous xenon.