Heavy superheated droplet detectors as a probe of spin-independent WIMP dark matter existence

At present, application of Superheated Droplet Detectors (SDDs) in WIMP dark matter searches has been limited to the spin-dependent sector, owing to the general use of fluorinated refrigerants which have high spin sensitivity. Given their recent demonstration of a significant constraint capability with relatively small exposures and the relative economy of the technique, we consider the potential impact of heavy versions of such devices on the spin-independent sector. Limits obtainable from a ${\mathrm{CF}}_3\mathrm{I}$-loaded SDD are estimated on the basis of the radiopurity levels and backgrounds already achieved by the SIMPLE and PICASSO experiments. With 34 kgd exposure, equivalent to the current CDMS, such a device may already probe to below ${10}^{-6}\mathrm{pb}$ in the spin-independent cross section.

Figure 1

Variation of $E_{\mathrm{thr}}^A$ with temperature for each of the ${\mathrm{CF}}_3\mathrm{I}$ components. The vertical line indicates the temperature below which $\alpha$’s are below the stopping power threshold of the detector.

Figure 2

Spin-independent exclusion plots for ${\mathrm{CF}}_3\mathrm{I}$, projected for 34 kgd exposure and 8 keV threshold recoil energy, or $37°\mathrm{C}$ and 2 atm operating temperature and pressure. The lower dashed contour assumes background discrimination with no residual events after the cut, while the upper dashed line assumes a $34\mathrm{evts}/\mathrm{kgd}$ 90% C.L. upper limit on the undiscriminated WIMP rate (see text).

Figure 3

Exclusion plots in the $g_p-g_n$ plane at $50\mathrm{GeV}/{\mathrm{c}}^2$. The projections for “no evt” (thick dash-dot) and “34 evt” (thick dash) 34 kgd ${\mathrm{CF}}_3\mathrm{I}$ SDD exposures are seen to contribute to the overall picture (the overall allowed region is shaded). The “lower limit” of DAMA/NaI is the inner boundary of its allowed shell.

Figure 4

Spin-dependent exclusions in the $a_p-a_n$ plane at $M_W=50\mathrm{GeV}/{\mathrm{c}}^2$, indicating the anticipated limits from “no evt” and “34 evt” 34 kgd ${\mathrm{CF}}_3\mathrm{I}$ measurements, with the spin matrix elements from Ref. 32; the dotted ellipse is a similar 34 kgd “no evt” projection using the spin matrix elements of Ref. 34.