Analysis of the low-energy electron-recoil spectrum of the CDMS experiment

TL;DR

This study analyzes the low-energy electron-recoil spectrum from the CDMS II experiment, finding no excess above background and setting limits that challenge interpretations of DAMA's modulation signal under certain assumptions.

Contribution

The paper provides the first detailed low-energy electron-recoil spectrum analysis from CDMS II and compares it to DAMA results, setting new upper limits on potential dark matter signals.

Findings

No significant excess above background in 2-8.5 keV range.

CDMS upper limits are significantly lower than DAMA's observed rate.

Constraints on dark matter interpretations of DAMA's modulation.

Abstract

We report on the analysis of the low-energy electron-recoil spectrum from the CDMS II experiment using data with an exposure of 443.2 kg-days. The analysis provides details on the observed counting rate and possible background sources in the energy range of 2 - 8.5 keV. We find no significant excess in the counting rate above background, and compare this observation to the recent DAMA results. In the framework of a conversion of a dark matter particle into electromagnetic energy, our 90% confidence level upper limit of 0.246 events/kg/day at 3.15 keV is lower than the total rate above background observed by DAMA by 8.9$\sigma$. In absence of any specific particle physics model to provide the scaling in cross section between NaI and Ge, we assume a Z^2 scaling. With this assumption the observed rate in DAMA differs from the upper limit in CDMS by 6.8$\sigma$. Under the conservative assumption that the modulation amplitude is 6% of the total rate we obtain upper limits on the modulation amplitude a factor of ~2 less than observed by DAMA, constraining some possible interpretations of this modulation.