Exclusion Limits on the WIMP-Nucleon Cross-Section from the Cryogenic Dark Matter Search

Abstract

The Cryogenic Dark Matter Search (CDMS) employs Ge and Si detectors to search for WIMPs via their elastic-scattering interactions with nuclei while discriminating against interactions of background particles. CDMS data give limits on the spin-independent WIMP-nucleon elastic-scattering cross-section that exclude unexplored parameter space above 10 GeV c^{-2} WIMP mass and, at > 84% CL, the entire 3$σ$ allowed region for the WIMP signal reported by the DAMA experiment.

Figures (4)

• Figure 1: Ionization yield ($Y$) vs. recoil energy for veto-anticoincident single scatters contained in the inner electrodes of the 3 uncontaminated Ge detectors. Solid curve: expected position of nuclear recoils. Dashed curves: nominal 90% nuclear-recoil acceptance region. Dashed line: 10 keV analysis threshold. Dashed-dotted curve: threshold for separation of ionization signal from amplifier noise. Circled points: nuclear recoils. The presence of 3 events just above the acceptance region is compatible with 90% acceptance.
• Figure 2: Solid: histogram of nuclear recoils observed in the inner electrodes of the 3 uncontaminated Ge detectors (left-hand scale). Shaded: 10 keV analysis threshold. Dashed: peak-normalized nuclear-recoil efficiency (right-hand scale).
• Figure 3: Scatter plot of ionization yields for multiple scatters in the 3 uncontaminated Ge detectors with at least 1 inner-electrode scatter and both scatters between 10 and 100 keV. Circled events are tagged as nuclear recoils in both detectors. Bulk recoils and surface events lie at $Y \simeq 1$ and $Y \sim 0.75$, respectively.
• Figure 4: Spin-independent $\sigma$ vs. $M$. The regions above the curves are excluded at 90% CL. Solid dark curve: limit from this analysis. Dotted curve: CDMS expected sensitivity (median simulated limit) given the observed neutron background. Because the number of multiple scatters observed is larger than expected, the limit from this analysis is lower than the median simulated limit. Solid light curve: DAMA limit using pulse-shape analysis DAMApsa. Shaded region: DAMA 3$\sigma$ allowed region as described in text DAMA2000. Dashed-dotted curve: Ge diode limit, dominated by hm. All curves are normalized following lewin, using the Helm spin-independent form-factor, $A^2$ scaling, WIMP characteristic velocity $v_0 = 220$ km s$^{-1}$, mean Earth velocity $v_E = 232$ km s$^{-1}$, and $\rho = 0.3$ GeV c$^{-2}$ cm$^{-3}$.