Low-Mass Dark Matter Search with CDMSlite (1707.01632v3)

Abstract: The SuperCDMS experiment is designed to directly detect weakly interacting massive particles (WIMPs) that may constitute the dark matter in our Galaxy. During its operation at the Soudan Underground Laboratory, germanium detectors were run in the CDMSlite mode to gather data sets with sensitivity specifically for WIMPs with masses ${<}$10 GeV/$c^2$. In this mode, a higher detector-bias voltage is applied to amplify the phonon signals produced by drifting charges. This paper presents studies of the experimental noise and its effect on the achievable energy threshold, which is demonstrated to be as low as 56 eV${\text{ee}}$ (electron equivalent energy). The detector-biasing configuration is described in detail, with analysis corrections for voltage variations to the level of a few percent. Detailed studies of the electric-field geometry, and the resulting successful development of a fiducial parameter, eliminate poorly measured events, yielding an energy resolution ranging from ${\sim}$9 eV${\text{ee}}$ at 0 keV to 101 eV${\text{ee}}$ at ${\sim}$10 eV${\text{ee}}$. New results are derived for astrophysical uncertainties relevant to the WIMP-search limits, specifically examining how they are affected by variations in the most probable WIMP velocity and the Galactic escape velocity. These variations become more important for WIMP masses below 10 GeV/$c^2$. Finally, new limits on spin-dependent low-mass WIMP-nucleon interactions are derived, with new parameter space excluded for WIMP masses $\lesssim$3 GeV/$c^2$

• The paper demonstrates that applying a high bias in CDMSlite amplifies phonon signals to achieve a 56 electron-equivalent energy threshold for low-mass WIMP detection.
• It introduces a detailed energy resolution model that accounts for electronic noise, statistical variations, and position-dependent effects to improve nuclear recoil identification.
• The study sets new exclusion limits for spin-dependent interactions below 3 GeV/c², guiding future experimental upgrades for detecting even lighter dark matter candidates.

Low-Mass Dark Matter Search with CDMSlite: A Comprehensive Analysis

This paper presents the results of a search for low-mass dark matter particles, specifically weakly interacting massive particles (WIMPs), using the CDMSlite operating mode of the SuperCDMS experiment. The paper focuses on WIMPs with masses less than 10 GeV/$c^2$. This analysis is significant due to the ongoing search for empirical evidence of dark matter, which constitutes a large portion of the Universe's mass-energy density as outlined by cosmological observations.

The SuperCDMS experiment employs germanium detectors operating at cryogenic temperatures, designed to measure tiny nuclear recoils caused by potential WIMP interactions. The CDMSlite mode enhances sensitivity for low-mass WIMPs by applying a higher detector-bias voltage. This bias amplifies phonon signals, thus lowering the energy thresholds required to detect WIMP-induced nuclear recoils. The paper reports a demonstrated energy threshold as low as 56 electron-equivalent (ee) energy, signifying significant sensitivity enhancements.

A distinct contribution of this paper lies in its comprehensive analysis of the energy resolution model. This model accounts for three primary factors—electronic noise, Fano factor induced statistical variations, and position-dependent signal modulations. Such careful calibration allows the experiment to accurately interpret potential dark matter signals amidst backgrounds primarily constituted by electron recoils.

Furthermore, the fidelity of the reported results could be affected by astrophysical uncertainties in the WIMP halo model. Varying parameters such as the local standard of rest velocity and the Galactic escape velocity could substantially influence the interpretation of WIMP signals, especially at lower masses.

Another highlight of this research is the spin-dependent interaction analysis, with this experiment setting new exclusion limits for such interactions for WIMP masses below 3 GeV/$c^2$. This further extends the relevance of the findings, given that most dark matter experiments focus primarily on spin-independent interactions.

The results serve as an impetus for improving both current experimental setups and theoretical models related to light dark matter particles. Future work on CDMSlite aims to refine detection capabilities potentially down to WIMP masses of 400 MeV/$c^2$, extending the horizon for dark matter searches at the upcoming SuperCDMS SNOLAB initiative.

The pursuit of dark matter detection is ongoing and evolving, with methodologies continuing to be improved in both experimental technique and theoretical models. The insights from this paper contribute valuable advances in constraining the low-mass dark matter hypothesis and emphasize the critical synergy between experimental physics and astrophysical modeling in modern cosmology.