Compatibility of DAMA Dark Matter Detection with Other Searches

TL;DR

The paper tackles the tension between DAMA's annual modulation signal and null results from other direct-detection experiments. It develops a phenomenological framework in which light WIMPs scatter off Na, leveraging Na's lower speed threshold, and explores two velocity distributions that can reproduce DAMA while remaining consistent with other limits: (i) a conventional Maxwellian halo with $m \sim 5$–$9$ GeV, and (ii) a Maxwellian halo plus a dark matter stream aligned with Galactic rotation. A model-fitting procedure assesses DAMA modulations in model-independent amplitudes and tests against CDMS, EDELWEISS, and CRESST constraints, revealing marginal compatibility under the standard halo but improved compatibility when a modest stream is included with $\xi_{\rm str} \approx 0.03$. The work makes testable predictions: detectors using light nuclei such as Si (CDMS-Soudan) and O (CRESST) can probe the proposed scenarios, and broader halo models could further widen the viable parameter space. Overall, it provides a concrete, testable path to reconcile DAMA with other searches through light-WIMP scenarios and halo substructure.

Abstract

We present two examples of velocity distributions for light dark matter particles that reconcile the annual modulation signal observed by DAMA with all other negative results from dark matter searches. They are: (1) a conventional Maxwellian distribution for particle masses around 5 to 9 GeV; (2) a dark matter stream coming from the general direction of Galactic rotation (not the Sagittarius stream). Our idea is based on attributing the DAMA signal to scattering off Na, instead of I, and can be tested in the immediate future by detectors using light nuclei, such as CDMS-II (using Si) and CRESST-II (using O).

Figures (6)

• Figure 1: Threshold speeds $v_{\rm thr}$ of several experiments and target nuclei. The DAMA Na threshold is lower than the CDMS-SUF Ge threshold for $m < 22.3$ GeV.
• Figure 2: Comparison of the DAMA annual modulation region with other direct detection bounds for spin-independent WIMP-proton interactions and a conventional dark halo. In (a) the 2-6 and 6-14 keVee DAMA bins and in (b) the 2-4 and 6-14 keVee DAMA bins were used. In the hatched region, the WIMP-proton cross section $\sigma_{\rm p}$ at WIMP mass $m$ reproduces the DAMA annual modulation results at the 90% and 3$\sigma$ C.L. (inner densely hatched region and outer hatched region, respectively). The region above each other line is excluded at 90% C.L. by the corresponding experiment (DAMA/NaI-96, CRESST-I and II, EDELWEISS, CDMS-SUF and CDMS-Soudan [denoted by CDMS-S.]). In (a), there is a region compatible with the DAMA annual modulation and all other experiments at the 3$\sigma$ but not the 90% C.L. In (b), there is a compatible region at the 90% C.L. also.
• Figure 3: Same as Fig. 2(a) but with the addition of a dark matter stream with density 3% of the conventional local halo density, heliocentric arrival direction of ecliptic coordinates $(\lambda_{\rm str}, \beta_{\rm str})=(340^\circ, 0^\circ)$, and heliocentric speed of (a) 300 km/s, (b) 600 km/s, (c) 900 km/s, and (d) 1200 km/s. The DAMA modulation region is shown both for the 90% and the 3$\sigma$ C.L. (inner densely hatched and outer hatched regions, respectively). The gaps in the DAMA modulation region in panels (c) and (d) are due to our requirement that $\chi^2_{\rm min}<2$. The experimental upper limits change when the stream is included.
• Figure 4: Range of WIMP masses $m$ for which there is a compatible region between the DAMA modulation and the other experimental results at various stream heliocentric speeds $v_{\rm str}$. Here the stream is assumed to arrive from ecliptic longitude $\lambda_{\rm str}=340^\circ$ and ecliptic latitude $\beta_{\rm str}=0^\circ$. Also indicated is the speed above which the stream is extragalactic (dashed horizontal line). The inner densely hatched and outer hatched regions correspond to the 90% and 3$\sigma$ C.L., respectively. In (a), we use the 2-6 and 6-14 keVee DAMA bins; in (b), the 2-4 and 6-14 keVee bins. At the 3$\sigma$ level it is possible to find WIMP masses compatible with DAMA and all other experiments at any assumed stream speed.
• Figure 5: Same as Fig. 4(a) at the 90% C.L. but showing the effect of changing the stream density from 3% to 2% and to 1% of the local smooth halo density.