Experimental constraints on a dark matter origin for the DAMA annual modulation effect

TL;DR

The paper uses a novel p-type point-contact (PPC) germanium detector to test whether the DAMA annual modulation can arise from a standard isothermal WIMP halo, reporting that this scenario is excluded at 90% CL across the relevant parameter space. It demonstrates the detector's sub-keV energy threshold, excellent resolution, and background rejection, enabling stringent limits on spin-independent WIMP-nucleus scattering for light WIMPs. It also constrains axio-electric coupling of dark pseudoscalars in a standard halo, challenging the pseudoscalar interpretation of DAMA. The analysis discusses NMSSM light neutralino scenarios and outlines the projected reach of a larger PPC array, highlighting complementarity with other searches and the potential to decisively test DAMA's claim and broader light-DM scenarios.

Abstract

A claim for evidence of dark matter interactions in the DAMA experiment has been recently reinforced. We employ a new type of germanium detector to conclusively rule out a standard isothermal galactic halo of Weakly Interacting Massive Particles (WIMPs) as the explanation for the annual modulation effect leading to the claim. Bounds are similarly imposed on a suggestion that dark pseudoscalars mightlead to the effect. We describe the sensitivity to light dark matter particles achievable with our device, in particular to Next-to-Minimal Supersymmetric Model candidates.

Figures (4)

• Figure 1: Improvements in threshold and resolution in a PPC design (bottom), compared to a typical coaxial HPGe twin (top). Cosmogenic peaks are clearly resolved in the PPC spectrum. BE stands for binding energy, EC for electron capture.
• Figure 2: Parameter space region (cross-hatched) able to explain the DAMA modulation via spin-independent couplings from an isothermal light-WIMP halo sigraciela. Lines delimit the coupling ($\sigma_{SI}$) vs. WIMP mass ($m_{\chi}$) regions excluded by relevant experiments sigraciela. All regions are defined at the 90% confidence level. Inset: PPC spectrum used for the extraction of present limits. Lines display the signals expected from some reference WIMP candidates (dotted: $m_{\chi}$= 8 GeV/c$^{2}$, $\sigma_{SI}=10^{-4}$pb. Dashed: $m_{\chi}$= 6 GeV/c$^{2}$, $\sigma_{SI}=0.002$ pb. Dash-dotted: $m_{\chi}$= 4 GeV/c$^{2}$, $\sigma_{SI}=10^{-2}$pb).
• Figure 3: Hatched region: viable parameter space in an interpretation of the DAMA modulation involving an axio-electric coupling $g_{a\bar{e} e}$ from pseudoscalars composing a dark isothermal halo, according to damapseudo. The validity of this interpretation is now challenged maxim (see text). The solid line indicates present limits, dashed lines recent astrophysical bounds georg. Inset: expected pseudoscalar interaction rates in Ge and NaI, for a fixed value of $g_{a\bar{e} e}$, as a function of pseudoscalar mass $m_{a}$.
• Figure 4: Solid lines: spin-independent sensitivity from leading experiments in the WIMP low-mass region. A theoretically-favored NMSSM phase space is denoted by crosses. Dashed lines: predicted sensitivity for PPC HPGe in a number of scenarios jcap: a) expected reduction in background from cryostat upgrade, b) background reduction to best achieved in HPGe igexdm plus an improvement to 100 eV threshold, c) very conservative limiting sensitivity imposed by $\sim$15 d of cosmogenic $^{3}$H production at sea level for the Majo-ra-na demonstrator array (a best estimate represents a $\times10$ further improvement).