Dark Matter Search Results Using the Silicon Detectors of CDMS II

We report results of a search for Weakly Interacting Massive Particles (WIMPs) with the silicon (Si) detectors of the CDMS II experiment. A blind analysis of data from eight Si detectors, with a total raw exposure of 140.2 kg-days, revealed three WIMP-candidate events with a final surface-event background estimate of 0.41 (-0.08 +0.20)(stat.) (-0.24 +0.28) (syst.). Other known backgrounds from neutrons and 206Pb are limited to < 0.13 and < 0.08 events at the 90% confidence level, respectively. These data place a 90% upper confidence limit on the WIMP-nucleon cross section of 2.4E-41 cm^2 at a WIMP mass of 10 GeV/c^2. Simulations indicate a 5.4% probability that a statistical fluctuation of the known backgrounds would produce three or more events in the signal region. A profile likelihood ratio test that includes the measured recoil energies of the three events gives a 0.19% probability for the known-background-only hypothesis when tested against the alternative WIMP+background hypothesis. The highest likelihood was found for a WIMP mass of 8.6 GeV/c^2 and WIMP-nucleon cross section of 1.9E-41 cm^2.