Silicon Detector Dark Matter Results from the Final Exposure of CDMS II

TL;DR

This paper reports a search for light WIMPs using silicon detectors in the CDMS II experiment, observing three candidate events with a low background estimate, suggesting a potential signal for dark matter particles around 8.6 GeV/c2.

Contribution

First detailed silicon detector search for low-mass WIMPs with a blind analysis, setting new constraints and indicating possible dark matter signals.

Findings

Observed three WIMP candidate events.

Estimated background of 0.41 events with uncertainties.

Best-fit WIMP mass of 8.6 GeV/c2 with cross section 1.9e-41 cm2.

Abstract

We report results of a search for Weakly Interacting Massive Particles (WIMPS) with the silicon detectors of the CDMS II experiment. This blind analysis of 140.2 kg-days of data taken between July 2007 and September 2008 revealed three WIMP-candidate events with a surface-event background estimate of 0.41^{+0.20}_{-0.08}(stat.)^{+0.28}_{-0.24}(syst.). Other known backgrounds from neutrons and 206Pb are limited to < 0.13 and <0.08 events at the 90% confidence level, respectively. The exposure of this analysis is equivalent to 23.4 kg-days for a recoil energy range of 7-100 keV for a WIMP of mass 10 GeV/c2. The probability that the known backgrounds would produce three or more events in the signal region is 5.4%. A profile likelihood ratio test of the three events that includes the measured recoil energies gives a 0.19% probability for the known-background-only hypothesis when tested against the alternative WIMP+background hypothesis. The highest likelihood occurs for a WIMP mass of 8.6 GeV/c2 and WIMP-nucleon cross section of 1.9e-41 cm2.