Limits on spin-dependent WIMP-nucleon interactions from the Cryogenic Dark Matter Search

The Cryogenic Dark Matter Search (CDMS) is an experiment to detect weakly interacting massive particles (WIMPs), which may constitute the universe’s dark matter, based on their interactions with Ge and Si nuclei. We report the results of an analysis of data from the first two runs of CDMS at the Soudan Underground Laboratory in terms of spin-dependent WIMP-nucleon interactions on ${}^{73}\mathrm{Ge}$ and ${}^{29}\mathrm{Si}$. These data exclude new regions of WIMP parameter space, including regions relevant to spin-dependent interpretations of the annual modulation signal reported by the DAMA/NaI experiment.

Figure 1

Upper limit contours (90% confidence level) for recent CDMS data sets, plotted in the cases of (left) pure neutron and (right) pure proton coupling. We show limits based on Ge (solid line) and Si (dash-dot line) from the combined Soudan data (black). Dashed curves represent Ge limits using the alternate form factor from [18]. As benchmarks, we also include interpretations of the DAMA/NaI annual modulation signal [10] (filled regions are $3\sigma$-allowed) and limits from other leading experiments: CRESST I [23] as computed in [11] (“$\times$”s), PICASSO [26] (squares), NAIAD [27] (circles), ZEPLIN I [28] (triangles), and Super-Kamiokande [29] (asterisks; an indirect search, based on different assumptions). EDELWEISS [30] and SIMPLE [31] report limits (not shown for clarity) comparable to CDMS Si and PICASSO, respectively. As a theoretical benchmark (see text), horizontal dotted lines indicate expected cross sections for a heavy Majorana neutrino. Plots courtesy of [32].

Figure 2

Regions in the $a_p-a_n$ plane allowed (at the 90% confidence level) by CDMS data. Each data set excludes the exterior of the corresponding ellipse. Two choices of WIMP mass $M_{\chi }$ are shown: $15\mathrm{GeV}/c^2$ (left) and $50\mathrm{GeV}/c^2$ (right). Dot-dashed ellipses represent Si limits, solid ellipses represent Ge limits, and dashed ellipses represent Ge limits using the alternate form factor. Also shown are the corresponding interpretations of the DAMA/NaI modulation signal (near-horizontal light (pink) filled bands are $3\sigma$-allowed). The thin dark (blue) filled wedges correspond to models satisfying $0.55<|\frac{a_n}{a_p}|<0.8$, a constraint from the effMSSM framework [16].