Search for Weakly Interacting Massive Particles with the First Five-Tower Data from the Cryogenic Dark Matter Search at the Soudan Underground Laboratory

We report results from the Cryogenic Dark Matter Search at the Soudan Underground Laboratory (CDMS II) featuring the full complement of 30 detectors. A blind analysis of data taken between October 2006 and July 2007 sets an upper limit on the weakly interacting massive particle (WIMP) nucleon spin-independent cross section of $6.6\times {10}^{-44}{\mathrm{cm}}^2$ ($4.6\times {10}^{-44}{\mathrm{cm}}^2$ when combined with previous CDMS II data) at the 90% confidence level for a WIMP mass of $60\mathrm{GeV}/c^2$. This achieves the best sensitivity for dark matter WIMPs with masses above $44\mathrm{GeV}/c^2$, and significantly restricts the parameter space for some favored supersymmetric models.

Figure 1

Ionization yield versus timing parameter (see text) for calibration data in one of our Ge detectors. The yield is normalized to unity for typical bulk-electron recoils (dots; from ${}^{133}\mathrm{Ba}$ $\gamma$-rays). Low-yield ${}^{133}\mathrm{Ba}$ events ($+$), attributed to surface electron recoils, are discriminated from neutron-induced nuclear recoils from ${}^{252}\mathrm{Cf}$ (○), based on timing parameter values. The vertical dashed line indicates the minimum timing parameter allowed for candidate dark matter events in this detector, and the box shows the approximate signal region, which is in fact weakly energy dependent.

Figure 2

Top: Ionization yield versus recoil energy in all detectors included in this analysis for events passing all cuts except the timing cut. The signal region between 10 and 100 keV recoil energies was defined using neutron calibration data and is indicated by the curved lines. Bulk-electron recoils have yield near unity and are above the vertical scale limits. Bottom: Same, but after applying the timing cut. No events are found within the signal region.

Figure 3

Spin-independent WIMP-nucleon (SI) and spin-dependent WIMP-neutron (SD) cross-section upper limits (90% C.L.) versus WIMP mass. In each panel, the curves represent 90% C.L. upper limits on the scattering cross section from this work and other recent experiments. Shaded regions represent parameter ranges expected from supersymmetric models described in [22, 23]. Data courtesy of [24].