Relic neutralinos and the two dark matter candidate events of the CDMS II experiment

TL;DR

The paper investigates whether relic neutralinos, within an effMSSM framework, can account for the two CDMS II candidate events while remaining compatible with the DAMA/LIBRA annual-modulation signal. It adopts an effective MSSM at the electroweak scale with independent parameters $M_1, M_2, M_3, \mu, \tan\beta, m_A, m_{\tilde q}, m_{\tilde l}$ and $A$, with nonunified gaugino masses to permit light neutralinos, and applies stringent experimental constraints including $Z$ invisible width, LEP/Tevatron searches, rare decays $BR(b \rightarrow s + \gamma)$ and $BR(B_s^{0} \rightarrow \mu^+ \mu^-)$, and $a_\mu$. The analysis finds that for $m_\chi$ in the ~8–12 GeV range, the CDMS II region overlaps with the DAMA/LIBRA regions within hadronic and astrophysical uncertainties, supporting a common light WIMP interpretation. The study also explores spectral-information analyses of the CDMS II recoil data with and without background, arguing that relic light neutralinos provide a coherent interpretation compatible with other constraints; subsequent CoGeNT results further bolster the light-WIMP scenario.

Abstract

The CDMS Collaboration has presented its results for the final exposure of the CDMS II experiment and reports that two candidate events for dark matter would survive after application of the various discrimination and subtraction procedures inherent in their analysis. We show that a population of relic neutralinos, which was already proved to fit the DAMA/LIBRA data on the annual modulation effect, could naturally explain the two candidate CDMS II events, if these are actually due to a dark matter signal.

Figures (3)

• Figure 1: $\xi \sigma_{\rm scalar}^{(\rm nucleon)}$ as a function of the WIMP mass. The (green) shaded regions denote the DAMA/LIBRA dama08 annual modulation regions, under the hypothesis that the effect is due to a WIMP with a coherent interaction with nuclei; the region delimitated by the solid line refers to the case where the channeling effect is not included, the one with a dashed contour to the case where the channeling effect is included direct. The (violet) band displays the region related to the two CDMS candidate events, obtained from the total rate in the whole energy window. The scatter plot represents supersymmetric configurations calculated with the model summarized in the Appendix, at a fixed representative set of values for the hadronic quantities. The (red) crosses denote configurations with a neutralino relic abundance which matches the WMAP cold dark matter amount (0.098 $\leq \Omega_{\chi} h^2 \leq$ 0.122), while the (blue) dots refer to configurations where the neutralino is subdominant ($\Omega_{\chi} h^2 <$ 0.098). The region covered by a (blue) slant hatching denotes the extension of the scatter plot upwards and downwards, when the hadronic uncertainties in the scattering coherent cross--section are included.
• Figure 2: The same as in Fig. \ref{['fig:CDMS2.ps']}, except that the (yellow) shaded regions compatible with the CDMS II candidate events are obtained by a maximal likelihood method applied to the differential energy recoil rate, under the hypothesis of negligible background. The contours refer to (from the internal to the external one) 68%, 90% and 95% C.L.
• Figure 3: The same as in Fig. \ref{['fig:CDMS2_like_noback.ps']}, but under the hypothesis of a backgound contribution as in Ref. Kopp:2009qt, normalized to 0.8 events in the whole energy window of CDMS II. The contours refer to (from the internal to the external one) 68% and 85% C.L.