CDMSlite: A Search for Low-Mass WIMPs using Voltage-Assisted Calorimetric Ionization Detection in the SuperCDMS Experiment (1309.3259v3)

Abstract: SuperCDMS is an experiment designed to directly detect Weakly Interacting Massive Particles (WIMPs), a favored candidate for dark matter ubiquitous in the Universe. In this paper, we present WIMP-search results using a calorimetric technique we call CDMSlite, which relies on voltage- assisted Luke-Neganov amplification of the ionization energy deposited by particle interactions. The data were collected with a single 0.6 kg germanium detector running for 10 live days at the Soudan Underground Laboratory. A low energy threshold of 170 eVee (electron equivalent) was obtained, which allows us to constrain new WIMP-nucleon spin-independent parameter space for WIMP masses below 6 GeV/c2.

• The paper demonstrates that voltage-assisted Luke-Neganov amplification in a germanium detector achieves a record 170 eV energy threshold for low-mass WIMP detection.
• It employs a rigorous analysis with a 98.5% signal efficiency above 110 eV, calibrated using 133Ba and 71Ge lines to minimize background noise.
• The study constrains WIMP-nucleon interactions below 6 GeV/c², challenging previous results and informing future low-mass dark matter explorations.

CDMSlite: A Search for Low-Mass WIMPs using Voltage-Assisted Calorimetric Ionization Detection in the SuperCDMS Experiment

The SuperCDMS collaboration reports on an investigation into Weakly Interacting Massive Particles (WIMPs), a prominent dark matter candidate, utilizing the CDMSlite approach, which employs voltage-assisted Luke-Neganov amplification of ionization energy. The research leverages a single 0.6 kg germanium detector operated over a 10-day period at the Soudan Underground Laboratory. This paper sets a new precedent in achieving a low energy threshold of 170 eV$_\text{ee}$, pertinent for probing the WIMP-nucleon spin-independent parameter space at sub-6 GeV/$c^2$ masses.

The CDMSlite mode amplifies phonon signals through a high bias voltage, enhancing sensitivity to nuclear-recoil energies, thereby allowing for the investigation of low-mass WIMPs potentially responsible for anomalous event rates noted in experiments such as DAMA, CoGeNT, and CRESST II. This research addresses critical limitations common in existing detection modalities, particularly at energy levels where electronic noise and background discrimination degrade detectability.

Operationally, the CDMSlite utilizes a germanium detector with a bias set to 69 V to differentiate between electronic and nuclear recoils, achieving a remarkable baseline resolution of 14 eV$_\text{ee}$. The Luke-Neganov phonon amplification method ensures that energy deposited by potential WIMPs can be detected with improved clarity, even at low recoil energies typical for lighter WIMPs.

The data analysis implemented a rigorous programm of events selection to eliminate background noise, achieving a 98.5% detection efficiency for signals above 110 eV$_\text{ee}$. The adjustments were corroborated by calibration using $^{133}$Ba and corroborated through long-term detector monitoring using $^{71}$Ge activation lines. The clear energy spectrum achieved allowed translation into nuclear-recoil equivalent energy, factoring in ionization yield models to mitigate systematic uncertainties.

Significantly, the results contribute to exclusion limits in the WIMP parameter space, notably for masses below 6 GeV/$c^2$. These findings challenge portions of previously suggested contours from CDMS II Si and CoGeNT data. The paper demonstrates the robust capacity of the CDMSlite mode by detailing findings based on a concise net exposure of 6.3 kg-days, achieved without background subtraction.

The research not only advances current understandings of dark matter but also sets a paradigm for future low-mass WIMP searches. The approach lays groundwork for subsequent deployments with increased exposure and refined background discrimination capabilities, particularly in initiatives like SuperCDMS SNOLAB where reduced environmental interference can offer heightened sensitivity to the subtle signatures of light WIMPs. As the field advances, these methods will form a foundational aspect of both theoretical exploration and experimental application in particle physics.