Dark Matter attempts for CoGeNT and DAMA

TL;DR

This paper assesses whether the CoGeNT annual modulation and DAMA/LIBRA signals can arise from dark matter scattering on nuclei within a unified framework. It employs a general DM–nucleus scattering formalism that covers elastic and inelastic processes, spin-dependent and spin-independent couplings, isospin violations, and light mediators, and it tests against CDMS, XENON100, SIMPLE, and related results under a standard halo model. The main finding is that no single DM interpretation can coherently explain both signals while satisfying all experimental bounds; only narrow, case-specific regions offer partial consistency, which are typically ruled out by other constraints. The work highlights the tension between modulation and rate data and suggests that the CoGeNT/DAMA hints are unlikely to be robust DM signals within the explored parameter space, though certain exotic scenarios can yield limited overlaps.

Abstract

Recently, the CoGeNT collaboration presented a positive signal for an annual modulation in their data set. In light of the long standing annual modulation signal in DAMA/LIBRA, we analyze the compatibility of both of these signal within the hypothesis of dark matter (DM) scattering on nuclei, taking into account existing experimental constraints. We consider the cases of elastic and inelastic scattering with either spin-dependent or spin-independent coupling to nucleons. We allow for isospin violating interactions as well as for light mediators. We find that there is some tension between the size of the modulation signal and the time-integrated event excess in CoGeNT, making it difficult to explain both simultaneously. Moreover, within the wide range of DM interaction models considered, we do not find a simultaneous explanation of CoGeNT and DAMA/LIBRA compatible with constraints from other experiments. However, in certain cases part of the data can be made consistent. For example, the modulation signal from CoGeNT becomes consistent with the total rate and with limits from other DM searches at 90% CL (but not with the DAMA/LIBRA signal) if DM scattering is inelastic spin-independent with just the right couplings to protons and neutrons to reduce the scattering rate on xenon. Conversely the DAMA/LIBRA signal (but not CoGeNT) can be explained by spin-dependent inelastic DM scattering.

Figures (9)

• Figure 1: Time binned CoGeNT data Aalseth:2011wp with the mean values subtracted for three energy ranges. We show the results of fitting a cosine function with a period of one year and arbitrary phase (blue thin curve), the best fit to modulation data only (green thick curve) with $m_\chi = 10.5$ GeV, and the best fit to the unmodulated data (magenta dashed curve) with $m_\chi = 8$ GeV. The corresponding $\chi^2$ values of the $0.5-0.9$ and $0.9-3$ keV bands are also shown.
• Figure 2: Left: regions in the DM mass--cross section plane for elastic spin-independent scattering at 90% and 99% CL from CoGeNT data Aalseth:2011wp using only the modulation data (green) or only the unmodulated rate (magenta). The corresponding best fit points are marked with triangles. For the fit to the unmodulated rate we assume that the total excess events (after subtraction of the L-shell peaks and a flat background) are explained by DM. The dashed curve corresponds to the 99% CL limit from CoGeNT unmodulated data requiring that not more events than observed are predicted. We also show the allowed regions from CoGeNT 2010 data Aalseth:2010vx. Right: unmodulated CoGeNT event spectrum and two predictions from DM. The solid (dashed) curve refers to elastic (inelastic) scattering with parameters as given in the legend.
• Figure 3: Allowed regions (90% and 99% CL) and limits (90% CL) in the DM mass--cross section plane for elastic spin-independent scattering. We use data from CoGeNT Aalseth:2011wp (modulated and unmodulated), DAMA/LIBRA Bernabei:2008yi modulation, CDMS low-threshold Ge Ahmed:2010wy, CDMS Si Akerib:2005kh, and XENON100 Aprile:2011hi. For DAMA/LIBRA we show the allowed regions for two illustrative assumptions on the quenching factor of sodium, for XENON100 we show the limit for two assumptions on the light-yield factor $L_{\rm eff}$.
• Figure 4: Allowed regions and limits at 90% CL in the DM mass--cross section plane for inelastic spin-independent scattering with a DM mass spitting $\delta= 25$ keV. We use data from CoGeNT Aalseth:2011wp (modulated and unmodulated), DAMA/LIBRA Bernabei:2008yi, CDMS low-threshold Ge Ahmed:2010wy, and XENON100 Aprile:2011hi.
• Figure 5: Left: $A^2_{\rm eff}/A^2$ defined in eq. \ref{['eq:Asq_eff']}, as a function of the ratio of DM coupling to neutron and proton for various elements. Right: regions (90% and 99% CL) and limits (90% CL) in the DM mass--cross section plane for elastic spin-independent scattering with $f_n/f_p = -0.7$. The cross section on the vertical axis corresponds to $\bar{\sigma}$ defined in eq. \ref{['eq:sigmabarSI']}. We use data from CoGeNT Aalseth:2011wp (unmodulated spectrum), DAMA/LIBRA Bernabei:2008yi, CDMS Ge low-threshold Ahmed:2010wy and Si Akerib:2005kh, XENON100 Aprile:2011hi, and SIMPLE Felizardo:2011uw.