A Search for WIMPs with the First Five-Tower Data from CDMS

Abstract

We report first results from the Cryogenic Dark Matter Search (CDMS II) experiment running with its full complement of 30 cryogenic particle detectors at the Soudan Underground Laboratory. This report is based on the analysis of data acquired between October 2006 and July 2007 from 15 Ge detectors (3.75 kg), giving an effective exposure of 121.3 kg-d (averaged over recoil energies 10--100 keV, weighted for a weakly interacting massive particle (WIMP) mass of 60 \gev). A blind analysis, incorporating improved techniques for event reconstruction and data quality monitoring, resulted in zero observed events. This analysis sets an upper limit on the WIMP-nucleon spin-independent cross section of 6.6$\times10^{-44}$ cm$^2$ (4.6$\times10^{-44}$ cm$^2$ when combined with previous CDMS Soudan data) at the 90% confidence level for a WIMP mass of 60 \gev. By providing the best sensitivity for dark matter WIMPs with masses above 42 GeV/c$^2$, this work significantly restricts the parameter space for some of the favored supersymmetric models.

Figures (4)

• 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 $^{133}$Ba gamma rays). Low-yield $^{133}$Ba events (+), attributed to surface electron recoils, have small timing parameter values, allowing discrimination from neutron-induced nuclear recoils from $^{252}$Cf ($\circ$), which show a wide range of 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. (Color online.)
• Figure 2: Nuclear-recoil acceptance efficiency for event-specific cuts (i.e. excluding discarded data periods) as a function of recoil energy, averaged over all detectors used in the current analysis, weighted by their individual livetimes. The four curves represent the cumulative efficiencies at various stages during the analysis, culminating with the final efficiency (bottom) used to generate Figure \ref{['fig:limit']}.
• Figure 3: Top: Ionization yield versus recoil energy in all detectors included in this analysis for events passing all cuts except the ionization yield and timing cuts. 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 4: Spin-independent WIMP-nucleon cross-section upper limits (90% C.L.) versus WIMP mass. The upper curve (dash-dot) is the result of a re-analysis ogburn of our previously published data. The upper solid line is the limit from this work. The combined CDMS limit (lower solid line) has the same minimum cross-section as XENON10 Angle:2007uj (dashed) reports, but has more sensitivity at higher masses. Parameter ranges expected from supersymmetric models described in baltzgondolo (grey) and roszkowskiruiztrotta are shown (95% and 68% confidence levels in green and blue, respectively). Data courtesy of Gaitskell:dmplotter.