New DAMA dark-matter window and energetic-neutrino searches

Recently, the DAMA/LIBRA Collaboration has repeated and reinforced their claim to have detected an annual modulation in their signal rate, and have interpreted this observation as evidence for dark-matter particles at the $8.2\sigma$ confidence level. Furthermore, it has also been noted that the effects of channeling may enable a weakly interacting massive particle (WIMP) that scatters elastically via spin-independent interactions from nuclei to produce the signal observed by DAMA/LIBRA without exceeding the limits placed by CDMS, XENON, CRESST, CoGeNT, and other direct-detection experiments. To accommodate this elastic-scattering explanation, however, the mass of the responsible dark-matter particle must be relatively light, $m_{\mathrm{DM}}\lesssim 10\mathrm{GeV}$. Such dark-matter particles will become captured by and annihilate in the Sun at very high rates, leading to a potentially large flux of GeV-scale neutrinos. We calculate the neutrino spectrum resulting from WIMP annihilations in the Sun and show that existing limits from Super-Kamiokande can be used to close a significant portion of the DAMA region, especially if the dark-matter particles produce tau leptons or neutrinos in a sizable fraction of their annihilations. We also determine the spin-dependent WIMP-nuclei elastic-scattering parameter space consistent with DAMA. The constraints from Super-Kamiokande on the spin-dependent scenario are even more severe—they exclude any self-annihilating WIMP in the DAMA region that annihilates 1% of the time or more to any combination of neutrinos, tau leptons, or charm or bottom quarks.

Figure 1

The factor by which the WIMP annihilation rate in the Sun is suppressed as a result of WIMP evaporation. For each WIMP mass, we used a spin-independent elastic-scattering cross section near the middle of the DAMA region (see the upper frame of Fig. 3). For WIMPs heavier than 4 GeV, the effect of evaporation is negligible.

Figure 2

The number of upward-going muon events per year in Super-Kamiokande from WIMPs annihilating in the Sun as a function of mass for an elastic-scattering cross section with protons of ${10}^{-40}{\mathrm{cm}}^2$, assuming 100% annihilation to the indicated channel. The upper and lower frames correspond to spin-independent and spin-dependent couplings, respectively. In each frame, the thin (blue) lines extending to the left denote the results neglecting the effects of WIMP evaporation. See text for more details.

Figure 3

The limit on a light WIMP’s spin-independent elastic-scattering cross section with nuclei from Super-Kamiokande for various choices of dominant annihilation modes. The upper frame contains the DAMA allowed region as calculated in the two-bin analysis of Ref. 5, while the lower frame uses the full spectral analysis with (dark hatched region) and without (light hatched region) the 2–2.5 keVee bin. Also shown are the limits from the CDMS [10], CRESST [11], CoGeNT [12], and XENON [13] collaborations. The dotted green lines are the constraints derived by demanding that the predicted total rates predicted by a given WIMP candidate do not exceed those observed by DAMA at the $2\sigma$ level in any energy bin.

Figure 4

The limit on a light WIMP’s spin-dependent elastic-scattering cross section with nuclei from Super-Kamiokande for various choices of dominant annihilation modes. The upper frame contains the DAMA allowed region as calculated following the two-bin analysis of Ref. 5, while the lower frame uses the full spectral analysis with (dark hatched region) and without (light hatched region) the 2–2.5 keVee bin. Also shown are the limits from the CDMS [40], CRESST [11], XENON [41], and COUPP [42] collaborations. The dotted green lines are the constraints derived by demanding that the predicted total rates predicted by a given WIMP candidate do not exceed those observed by DAMA at the $2\sigma$ level in any energy bin.